[1] Current estimates of plasma parameters in the local interstellar medium indicate that the speed of the interstellar wind, i.e. the relative speed of the local interstellar cloud with respect to the Sun, is most likely less than both the fast magnetosonic speed (subfast) and the Alfvén speed (sub-Alfvénic), but greater than the slow magnetosonic speed (superslow). In this peculiar parameter regime, MHD theory postulates a slow magnetosonic shock ahead of the heliosphere, provided that the angle between the interstellar magnetic field and the interstellar plasma flow velocity is quite small (e.g. 15° to 30°). In this likely scenario, our multi-fluid MHD model of the heliospheric interface self-consistently produce a spatially confined quasi-parallel slow bow shock. Voyager 1 is heading towards the slow bow shock, while Voyager 2 is not, which means that the two spacecraft are expected to encounter different interstellar plasma populations beyond the heliopause. The slow bow shock also affects the density and spatial extent of the neutral hydrogen wall.

[1] Long-term 10-minute wind tower data and ceilometer backscatter data at Cabauw in the Netherlands provide quantitative information on the influence of low clouds on the diurnal evolution of the near-surface wind speed (NSWS) probability distribution (pdf), the wind power density (WPD), and their vertical structure in the bottom 200 m of the atmosphere. Under clear sky conditions, pronounced diurnal cycles are identified in the leading three moments of NSWS as well as WPD and the boundary layer thermal structure in all seasons. When low clouds are present, weaker diurnal cycles with a different vertical structure are observed. Under clear skies, skewness at night is positive within the stable air near the surface but negative above 100 m. In the presence of low clouds, wind speeds are positively skewed and the probability of strong winds is higher associated with a larger geostrophic wind speed.

[1] We assess the effect of high thermal conductivity of Earth's core, which was recently determined to be 2–3 times higher than previously thought, on Earth's thermo-chemical-magnetic evolution using a coupled model of simulated mantle convection and parameterized core heat balance, following the best-fit case of Nakagawa and Tackley [2010]. The value of core thermal conductivity has no effect on mantle evolution. The core-mantle boundary (CMB) heat flow starts high and decreases with time to ~13 TW, which is below the core adiabatic heat flux for the largest thermal conductivity tested (200 W/m/K), meaning that a purely thermal dynamo is not viable. However, gravitational energy release and latent heat associated with inner core growth become important in the last ~0.9 Gyr and allow continuous geodynamo generation despite high core thermal conductivity, although we estimate a subadiabatic region at the top of the core of order 100 s km.

[1] Tropospheric ozone is known to have a damaging effect on carbon uptake in the terrestrial biosphere. We show that limitations of available nitrogen for sufficient plant growth reduce the negative impact of tropospheric ozone on carbon uptake in plants, leading to a smaller indirect change in radiative forcing than previously calculated. Transient climate simulations between 1900 and 2004 where plant growth is affected by tropospheric ozone have been performed by the NCAR Community Land Model (CLM4) with and without a coupling to the nitrogen cycle. When the land model includes nitrogen limitation on plant growth, the negative effect from tropospheric ozone on carbon uptake in plants is reduced by up to a factor of four compared to model simulation without nitrogen limitation. Only 2–5% of the radiative forcing from CO₂ between 1900 and 2004 can be attributed to the indirect effect of tropospheric ozone which is a factor of six lower than results from previous studies.

[1] This study investigates El Niño precursors in a high-resolution version of CCSM3.5. First, using an Empirical Orthogonal Function (EOF) analysis of all non-ENSO tropical Pacific variability, we find that the Pacific Meridional Mode (PMM) acts as an ENSO trigger 7–9 months prior to large El Niño events in the model, which is consistent with previous model and observational studies. However, because not every PMM event triggers an ENSO event, we also find that PMM appears to be an effective trigger when the western-to-central Pacific is preconditioned (i.e. anomalously high sea surface heights or heat content). Second, this study looks at the contribution of western Pacific variability, namely WWBs, as well as all other non-ENSO variability in the tropical Pacific. We find that the relative importance of low frequency climate variability associated with PMM dominates over other non-ENSO variability between 15°N and 15°S, including high frequency atmospheric variability and WWBs, in acting as a precursor to El Niño events.

[1] Deforestation on Amazonia and central Brazil Cerrado could change regional climate, possibly shifting forest equilibrium into a bioclimatic envelope typical of savannas. Although impacts of climate change induced by deforestation are likely to vary sub-regionally, the potential geographic variation of these effects and the thresholds of rainforest and Cerrado removal that will affect Amazonian bioclimatic equilibrium remain unknown. We evaluate the effects of deforestation scenarios of increasing severity on the bioclimatic equilibrium of Amazon sub-regions. Results indicate that sub-regional precipitation responds in three distinct ways to progressive deforestation: a near-constant rate of reduction; a rapid drop for low deforestation levels; and a decrease after intermediate deforestation levels. Additionally, while inner forest regions remain inside rainforest bioclimatic envelope, outer forest regions may cross forest-savanna bioclimatic threshold even at low deforestation levels. We argue that at least 90% of Amazonia and 40% of Cerrado should be sustained to avoid sub-regional bioclimatic savannization.

[1] The properties of contrail cirrus clouds are retrieved through analysis of Terra and Aqua MODerate-resolution Imaging Spectroradiometer data for 21 cases of spreading linear contrails. For these cases, contrail cirrus enhanced the linear contrail coverage by factors of 2.4 – 7.6 depending on the contrail mask sensitivity. In dense air traffic areas, linear contrail detection sensitivity is apparently reduced when older contrails overlap and thus is likely diminished during the afternoon. The mean optical depths and effective particle sizes of the contrail cirrus were 2–3 times and 20% greater, respectively, than the corresponding values retrieved for the adjacent linear contrails. When contrails form below, in, or above existing cirrus clouds, the column cloud optical depth is increased and particle size is decreased. Thus, even without increased cirrus coverage, contrails will affect the radiation balance. These results should be valuable for refining model characterizations of contrail cirrus needed to fully assess the climate impacts of contrails.

[1] Microseisms are ground vibrations caused largely by ocean gravity waves. Multiple spatially separate noise sources may be coincidentally active. A method for source separation and individual wavefield retrieval of microseisms using a single pair of seismic stations is introduced, and a method of back-azimuth estimation assuming Rayleigh wave arrivals of microseisms is described. These methods are combined to separate and locate sources of microseisms in a synthetic model, and then applied to field microseismic recordings from Ireland in the North-East Atlantic. It is shown that source separation is an important step prior to location for both accurate microseism locations and microseisms wavefield studies.

[1] Delta margins are subject to relatively high rates of land subsidence and have the potential to significantly exacerbate future changes in sea levels predicted by global warming models used in impact studies. Through a combined analysis of GPS and persistent scatterer interferometry data, we determine that most of the coastline of Alexandria has been subject to moderate land subsidence over the past decade (0.4 mm/year on average and up to 2 mm/year locally). This contrasts to previous studies that suggested subsidence in excess of 3 mm/year. Based on our findings, we infer that on multi-century to millennia timescales, land subsidence in the area of Alexandria is dominated by tectonic setting and earthquakes or gravitational collapse episodes of a growth fault, whereas on shorter inter-seismic decadal to century timescales, subsidence rates are likely steady and moderate, in agreement with natural compaction and dewatering of the observed Holocene sediment layer.

[1] Strong diurnal variability of aerosol has been observed frequently for many urban/industrial regions. How this variability may alter the direct aerosol radiative forcing (DARF), however, is largely unknown. To quantify changes in the time-averaged DARF, we perform an assessment of 29 days of high temporal resolution ground-based data collected during the Two-Column Aerosol Project (TCAP) on Cape Cod, which is downwind of metropolitan areas. We demonstrate that strong diurnal changes of aerosol loading (about 20% on average) have a negligible impact on the 24-h average DARF when daily averaged optical properties are used to find this quantity. However, when there is a sparse temporal sampling of aerosol properties, which may preclude the calculation of daily averaged optical properties, large errors (up to 100%) in the computed DARF may occur. We describe a simple way of reducing these errors, which suggests the minimal temporal sampling needed to accurately find the forcing.

[1] We present the first observations of large amplitude waves in a well-defined electron diffusion region based on the criteria described by [36] at the sub-solar magnetopause using data from one THEMIS satellite. These waves identified as whistler mode waves, electrostatic solitary waves, lower hybrid waves and electrostatic electron cyclotron waves, are observed in the same 12-s waveform capture and in association with signatures of active magnetic reconnection. The large amplitude waves in the electron diffusion region are coincident with abrupt increases in electron parallel temperature suggesting strong wave heating. The whistler mode waves which are at the electron scale and enable us to probeelectron dynamics in the diffusion region were analyzed in detail. The energetic electrons (~30 keV) within the electron diffusion region have anisotropic distributions with T_e ⊥/T_e ∥ > 1 that may provide the free energy for the whistler mode waves. The energetic anisotropic electrons may be produced during the reconnection process. The whistler mode waves propagate away from the center of the “X-line” along magnetic field lines, suggesting that the electron diffusion region is a possible source region of the whistler mode waves.

[1] The reactive-infiltration instability, which develops when a porous matrix is dissolved by a flowing fluid, contains two important length scales. Here we outline a linear stability analysis that simultaneously incorporates both scales. We show that the commonly used “thin-front” model is a limiting case of a more general theory, which also includes convection-dominated dissolution as another special case. The wavelength of the instability is bounded from below, and lies in the range 1mm to 1km for physically reasonable flow rates and reaction rates. We obtain a closed form for the growth rate when the change in porosity is small.

[1] For the first time we quantify relationships between the Southern Ocean cyclones and large-scale atmospheric variability indices: the Southern Annular Mode (SAM), the El Niño–Southern Oscillation (ENSO), the Zonal Wave 3 Pattern (ZW3) and the Semi–Annual Oscillation (SAO). Using the ERA-Interim 1979–2011 results, we identify cyclones south of 40˚S and calculate monthly sectoral cyclone budgets of the Southern Ocean, defined as cyclogenesis minus cyclolysis plus net movement of cyclones into each sector. The SAM index has a strong connection with cyclones across all sectors. Positive SAM values are related to decreased eastward and increased southward movement of cyclones, resulting in higher cyclone densities along the Antarctic coast. The ENSO index shows strong associations with the cyclone behavior in the Amundsen–Ross Seas, whereas other regions are less sensitive to it. The ZW3 index has a stronger association with the meridional movement of cyclones than other indices.

[1] The Barents Oscillation (BO) is an anomalous wintertime atmospheric circulation pattern in the Northern Hemisphere that has been linked to the meridional flow over the Nordic Seas. There are speculations that the BO has important implications for the Arctic climate; however, it has also been suggested that the pattern is an artifact of Empirical Orthogonal Function (EOF) analysis due to an eastward shift of the Arctic Oscillation/North Atlantic Oscillation (AO/NAO). In this study, EOF analyses are performed to show that a robust pattern resembling the BO can be found during different time periods, even when the AO/NAO is relatively stationary. This “BO” has a high and stable temporal correlation with the geostrophic zonal wind over the Barents Sea, while the contribution from the AO/NAO is small. The surface air temperature anomalies over the Barents Sea are closely associated with this mode of climate variability.

[1] Knowledge of the relationship between bottom pressure p_b and sea level ζ is important for understanding ocean circulation and climate. We use recent Gravity Recovery and Climate Experiment (GRACE) Release-05 data along with altimetry toinvestigate the relationship between ζ and p_b over long periods (> 1 yr) and large scales (> 750 km). Elevated p_b signals are observed over deep extratropical regions (e.g., Southern Ocean basins) and shallow or semi-enclosed areas (e.g., Indonesian and Nordic seas). In these places, considerable ζ variance is explained by p_b variance. Correlation between ζ and p_b is significant in many regions, including instances of significant negative correlation suggestive of active baroclinic processes. Results exemplify the good quality of GRACE Release-05 data and demonstrate that contemporary regional ζ variability cannot always be interpreted in terms of steric changes alone.

[1] Enhanced snowfall on the East Antarctic ice sheet is projected to significantly mitigate 21st century global sea level rise. In recent years (2009 and 2011), regionally extreme snowfall anomalies in Dronning Maud Land, in the Atlantic sector of East Antarctica, have been observed. It has been unclear, however, whether these anomalies can be ascribed to natural decadal variability, or whether they could signal the beginning of a long-term increase of snowfall. Here we use output of a regional atmospheric climate model, evaluated with available firn core records and gravimetry observations, and show that such episodes had not been seen previously in the satellite climate data era (1979). Comparisons with historical data that originate from firn cores, one with records extending back to the 18th century, confirm that accumulation anomalies of this scale have not occurred in the past ~60 years, although comparable anomalies are found further back in time. We examined several regional climate model projections, describing various warming scenarios into the 21st century. Anomalies with magnitudes similar to the recently observed ones were not present in the model output for the current climate, but were found increasingly probable toward the end of the 21st century.

[1] The source-rupture process of the 2011 Ibaraki-oki earthquake was estimated from the joint inversion of the strong-motion and global positioning system (GPS) data. The estimated seismic moment and maximum slip are 2.8 × 10²⁰ Nm (M_xtrmw 7.9) and 6.3 m, respectively. The total rupture duration is approximately 30 s. The derived source model has one large slip area, which is surrounded by the subducted seamount and the northeastern edge of the Philippine Sea plate. From thismodel, we concluded that the rupture propagation of the 2011 Ibaraki-oki earthquake was stopped by the seamount and the Philippine Sea plate. We also showed the possibility of the rupture of this event being the reactivation of the preexisting asperityof an event that occurred in 1923.

[1] This article aims at quantifying the improvement in climate prediction skill as a function of temporal (from monthly to decadal) and spatial scales (from grid-point to global) when initializing a perturbed parameter ensemble of the Hadley Centre Climate Model. The focus is on near surface temperature and precipitation in the tropical band, the Northern and Southern hemispheres. For temperature, the forecast system reproduces the dominant impact of the external forcing at global spatial scale and at decadal time scales. There are significant improvements with initialization for the first 40 forecast months in the global and tropical domains. In the Northern (Southern) hemisphere, the initialization increases the skill in the first 12 (20) months on regional but not hemispheric scales. The initialization has a stronger impact in the model variants with a weaker global-mean temperature trend. For precipitation, the initialization corrects the negative correlation found at global and tropical scales.

[1] Satellite observations reveal a greening of the globe over recent decades. The role in this greening of the ‘CO₂ fertilization’ effect – the enhancement of photosynthesis due to rising CO₂ levels – is yet to be established. The direct CO₂ effect on vegetation should be most clearly expressed in warm, arid environments where water is the dominant limit to vegetation growth. Using gas exchange theory, we predict that the 14% increase in atmospheric CO₂ (1982–2010) led to a 5 to 10% increase in green foliage cover in warm, arid environments. Satellite observations, analysed to remove the effect of variations in rainfall, show that cover across these environments has increased by 11%. Our results confirm that the anticipated CO₂ fertilization effect is occurring alongside ongoing anthropogenic perturbations to the carbon cycle and that the fertilisation effect is now a significant land surface process.

[1] Stalagmite δ¹⁸Ο series currently provide the most robustly dated characterisation of glacial terminations. However, uncertainties associated with the stalagmite δ¹⁸Ο proxy record arise due to the complexity of flow within karst aquifers. Here we use an integrated climate-soil-groundwater lumped parameter hydrological model to demonstrate the range of potential stalagmite δ¹⁸Ο hydrological responses to significant global climate changes. Pseudoproxy stalagmite δ¹⁸Ο series were generated for millennial length model simulations, using GCM time-slice data for 12 ka, 11 ka, and 10 ka for eastern China. Our model demonstrates that the variability within published δ¹⁸Ο records from Chinese stalagmites falls within that of modelled pseudoproxy series. We utilise model output to: i. quantify hydrological uncertainty (specifically the relative importance of changing precipitation amount, isotopic composition and water balance); ii. identify any non-stationarity in δ¹⁸O variability and its relationship to climate change; and iii. demonstrate the processes that produce low-frequency power in stalagmite δ¹⁸Ο.

[1] Detection of volcanic plumes, especially ash-laden ones, is important both for public health and aircraft safety. A variety of geophysical tools and satellite data are used to monitor volcanic eruptions and to predict the movement of ash. However satellite-based methods are restricted by time of day and weather, while radars are often unavailable because of cost/portability. Here a method is proposed to detect volcanic plumes using GPS signal strength data. Strengths and limitations of the method are assessed using GPS data collected during the 2008 and 2009 eruptions of the Okmok and Mt. Redoubt volcanoes. Plume detections using this GPS technique are consistent with independently collected seismic and radar data.

[1] We investigated the Venus O₂ visible nightglow with imagery from the Venus Monitoring Camera on Venus Express. Drawing from data collected between April 2007 and January 2011, we study the global distribution of this emission, discovered in the late 70s by the Venera 9 and 10 missions. The inferred limb-viewing intensities are on the order of 150 kiloRayleighs at the lower latitudes and seem to drop somewhat towards the poles. The emission is generally stable, although there are episodes when the intensities rise up to 500 kR. We compare a set of Venus Monitoring Camera observations with coincident measurements of the O₂ nightglow at 1.27 μm made with the Visible and Infrared Thermal Imaging Spectrometer, also on Venus Express. From the evidence gathered in this and past works, we suggest a direct correlation between the instantaneous emissions from the two O₂ nightglow systems. Possible implications regarding the uncertain origin of the atomic oxygen green line at 557.7 nm are noted.

[1] We validate that changes of ground deformation recorded by GPS contain useful information for earthquake forecasting. A moving rate of variation (MRV) filter is used to extract short-term signals from GPS time series in New Zealand, California and Japan. The precursory information of these signals for large earthquakes is evaluated using Molchan's error diagram. The results suggest that the GPS signals provide a probability gain of 2 ∼ 4 for forecasting large earthquakes against a Poisson model. Further tests show that the GPS signals are not triggered by large earthquakes, and that the probability gain is not derived from forecasting aftershocks. This demonstrates that non-catalog information, such as GPS data, can be used to augment probabilistic models based on seismic catalog data, to improve forecasting of large earthquakes.

[1] Space geodetic observations of polar motion show that around 2005, the average annual pole position began drifting towards the east, an abrupt departure from the drift direction seen over the past century. Satellite gravity measurements from the Gravity Recovery and Climate Experiment (GRACE) show that about 90% of this change is due to accelerated melting of polar ice sheets and mountain glaciers and related sea level rise. The close relationship between long-term polar motion and climate-related mass redistribution established using GRACE data indicates that accurately measured polar motion data offer an additional tool for monitoring global-scale ice melting and sea level rise, and should be useful in bridging the anticipated gap between GRACE and follow-on satellite gravity missions.

[1] Simulations with the Global Ionosphere Plasmasphere (GIP) model driven by Whole Atmosphere Model (WAM) winds show significant longitudinal and day-to-day variations in the ionospheric parameters. Under fixed solar and geomagnetic activity levels, the contributions of lower atmosphere tides to the longitudinal and day-to-day variability in the upper atmosphere are estimated. Larger relative variability is found in the nighttime than in the daytime, which is consistent with observations. The perturbations from the lower atmosphere contribute about half of the observed variability in the ionospheric F₂ peak plasma density under moderate solar activity and geomagnetic quiet conditions. The daily variability of the equatorial vertical plasma drifts is primarily driven by the day-to-day amplitude changes of the migrating semidiurnal tide (SW2), while the wave-4 and wave-3 longitudinal variations during September are dominated by the non-migrating diurnal eastward propagating tides with zonal wave numbers 3 (DE3) and 2 (DE2), respectively.

[1] It has previously been suggested that ionospheric perturbations triggered by large dip-slip earthquakes might offer additional source parameter information compared to the information gathered from land observations. Based on 3D modeling of GPS- and GLONASS-derived total electron content (TEC) signals recorded during the 2011 Van earthquake (thrust, intra-plate event, M_w = 7.1, Turkey), we confirm that coseismic ionospheric signals do contain important information about the earthquake source, namely its slip mode. Moreover, we show that part of the ionospheric signal (initial polarity and amplitude distribution) is not related to the earthquake source, but is instead controlled by the geomagnetic field and the geometry of the GNSS satellites constellation. Ignoring these non-tectonic effects would lead to an incorrect description of the earthquake source. Thus, our work emphasizes the added caution that should be used when analyzing ionospheric signals for earthquake source studies.

[1] We examined possible responses of cyclone activities to the bimodal path states of the Kuroshio Current (i.e., large-meander (LM) and non-LM (NLM)) by using the long-term reanalysis data and the twentieth century hindcast experiment of atmosphere–ocean coupled model. Compared with a seasonal mean cyclone track frequency for the LM and NLM periods, a primary cyclone track shifts southward in association with the meander of Kuroshio Current. Composite analyses of the hindcast experiment showed remarkable atmospheric responses accompanying the Kuroshio LM. The Kuroshio LM causes a decrease in latent heat flux in the south of Japan and a southward shift of the near-surface baroclinic zone. Distinctive decreases in thermodynamic fluxes inhibit the rapid development of cyclones in the meander region, eventually inducing positive sea level pressure anomalies downstream from that region.

[1] A coupled CGCM, and an uncoupled AGCM forced with the SST and external forcing of the coupled model, simulate similar two meter air temperature (TS) trends and also similar sea level pressure (SLP) trends for the latter half of the 20th century. This suggests that the inability of atmospheric models forced by observed SST and external forcing to reproduce observed SLP trends in the Indian Ocean could be due to model bias rather than lack of coupling. The internally generated TS trend in the CGCM is found to be small in comparison to the externally forced component. Intrinsic atmospheric noise explains most of the CGCM's internally generated high latitude SLP trend, while in low latitudes the response of the SLP trend to the internally generated SST trend is important.

[1] The Main Development Region (MDR) for tropical cyclones (TCs) in the western North Pacific Ocean is the most active TC region in the world. Based on synergetic analyses of satellite altimetry and gravity observations, the subsurface ocean conditions in the western North Pacific MDR has become even more favorable for typhoon and super-typhoon intensification. Compared to the early 1990s, a 10% increase in both the depth of the 26 °C isotherm (D26) and Tropical Cyclone Heat Potential (TCHP) has occurred in the MDR. In addition, the areas of high TCHP

[2] (≥ 110 kJ cm^-2) and lager D26 (≥ 110 m) have 13% and 17% increases, respectively. These high TCHP and lager D26 regions are often associated with intensification to super-typhoon intensity.

[1] Two and three-dimensional simulations are used to explore the effects of continental distribution on mantle convection. In both 2D and 3D, at total surface areas < 50%, internal temperature is weakly sensitive to continental configuration. Mantle heat flux values show mild variations with changing configuration. In 3D, at total continental area > 50%, the dependence of mantle heat loss on continental configuration becomes stronger. Mantle temperature continues to increase with total continental area, but now varies by 5–7% with changing configurations. When distributed, continents can cause flow patterns to become locked. This leads to significant variations in mantle temperature below continental and oceanic regions. This differs from the expectation that supercontinents would preferentially lead to large lateral variations in mantle temperatures and suggests that insulation induced thermal anomalies could exist below continents today, if they have remained fixed relative to mantle flow (e.g. Africa).

[1] Slow slip behaviors are suggested to have a close correlation with the presence of excess pore fluid pressure. In this study we conducted deformation experiments with and without excess pore pressure on intact porous sandstone samples to investigate effect of pore fluid pressure on rupture growth and slip instability. Experimental conditions are such that the samples failed either in brittle faulting or transitional regimes. The experimental results indicate that in the brittle faulting regime prone to seismic deformation, excess pore pressure causes reduction in brittle strength but no detectable difference in slip behavior compared to the cases without excess pore pressure. In the transitional regime, which is prone to stable deformation, excess pore pressure induces slip instability on otherwise stable sliding faults, but there are measurable differences compared to the unstable slip in the brittle faulting regime due to the interaction between unstable crack growth and dilatancy hardening.

[1] A global estimate of the water-mass transformation by internal wave driven mixing in the deep ocean is presented. The estimate is based on the energy conversion from tidal and geostrophic motions into internal waves combined with a turbulent mixing parameterization. We show that internal wave driven mixing in the deep ocean can sustain 20-30 Sv of water mass transformation. One third or more of this transformation is attributed to lee waves generated by geostrophic motions flowing over rough topography, primarily in the Southern Ocean. While these results are uncertain due to many assumptions, poorly constrained parameters and data noise that enter in the calculation, the result that lee wave driven mixing plays an important role on the abyssal ocean circulation is likely robust. The implication is that lee wave driven mixing should be represented in ocean and climate models, but currently it is not.

[1] The rate of increase of global-mean surface air temperature (SAT_g) has apparently slowed during the last decade. We investigated the extent to which state-of-the-art general circulation models (GCMs) can capture this hiatus period by using multi-model ensembles of historical climate simulations. While the SAT_g linear trend for the last decade is not captured by their ensemble means regardless of differences in model generation and external forcing, it is barely represented by an 11-member ensemble of a GCM, suggesting an internal origin of the hiatus associated with active heat uptake by the oceans. Besides, we found opposite changes in ocean heat uptake efficiency (κ), weakening in models and strengthening in nature, which explain why the models tend to overestimate the SAT_g trend. The weakening of κ commonly found in GCMs seems to be an inevitable response of the climate system to global warming, suggesting the recovery from hiatus in coming decades.

[1] Observations of polar mesospheric clouds by the Aeronomy of Ice in the Mesosphere (AIM) Explorer show that for the Northern summers of 2007-2010, the cloud ice water content (IWC) and occurrence frequency varied with the meteorological forcing from the Southern winter stratosphere. With the increase in solar flux in the last two years, expectations were that the clouds would decrease due to reduced water vapor (H₂O) and/or higher temperatures. Surprisingly, we observe more clouds in 2011 and 40% greater IWC in 2011 and 2012. The increase is particularly pronounced in the clouds with highest IWC. These high IWC clouds are associated with significant enhancements in total H₂O (vapor and ice). We suggest this implies an additional source of H₂O and that this is provided by space traffic exhaust. A preliminary estimate of the H₂O released from summertime space traffic over the last six years is qualitatively consistent with this suggestion.

[1] Measurements of gaseous (NO, NO_y, SO₂, HONO) and ice particle concentrations in young contrails in primary and secondary wakes of aircraft of different sizes (B737, A319, A340, A380) are used to investigate ice particle formation behind aircraft. The gas concentrations are largest in the primary wake and decrease with increasing altitude in the secondary wake, as expected for passive trace gases and aircraft-dependent dilution. In contrast, the measured ice particle concentrations were found larger in the secondary wake than in the primary wake. The contrails contain more ice particles than expected for previous black carbon (soot) estimates. The ice concentrations may result from soot induced ice nucleation for a soot number emission index of 10¹⁵ kg^-1. For a doubled ice particle concentration in young contrails, a contrail cirrus model computes about 60% increases of global radiative forcing by contrail cirrus because of simultaneous increases in optical depth, age and cover.

[1] Eruptive activity of individual monogenetic volcanoes usually lasts few days or weeks. However, their short lifetime does not always means that their dynamics and structure are simple. Monogenetic cones construction is rarely witnessed from the beginning to the end and conditions for observing their internal structure are hardly reached. We provide high-resolution electrical resistivity sections (10 m electrode spacing) of three monogenetic cones from north-eastern Spain, comparing our results to geological observations to interpret their underground continuation. The 100 m maximum depth of exploration provides information on almost the entire edifices, highlighting the relationships between Strombolian and hydromagmatic deposits in two multi-phases edifices. A main observation is a column of distinct resistivity centered on the Puig d'Adri volcano, which we interpret as the eruptive conduit. This method can provide valuable information on the past volcanic dynamics of monogenetic volcanic fields, which has real implications for the forecast of future activity.

[1] We investigate a direct south-north crossing of a reconnection ion diffusion region in the magnetotail. During this crossing, multiple electron density dips with a further density decrease within the cavity, called sub-cavities, adjacent to the northern separatrix are observed. The correlation between electron density sub-cavities and strong electric field fluctuations is obvious. Within one of the sub-cavities, a series of very strong oscillating perpendicular electric field and patchy parallel electric field are observed. The parallel electric field is nearly unipolar and directs away from X-line. In the same region, inflow electrons with energy up to 100 keV are injected into the X-line. Based on the observations, we conclude that the high energy inflowing electrons are accelerated by the patchy parallel electric field. Namely, electrons have been effectively accelerated while they are flowing into the X-line along the separatrix. The observations indicate that electron acceleration region is widely larger than the predicted electron diffusion region in the classical Hall magnetic reconnection model.

[1] We examine the ocean mixed layer response to intraseasonal atmospheric forcing using moored time series data in the central equatorial Indian Ocean for October 2004 to March 2005, a period coincident with two active phases of the Madden-Julian Oscillation (MJO). Both MJO events were accompanied by an SST decrease that was partially the consequence of reduced net surface heat flux. In addition, during the first event in October-November 2004, advection by an enhanced Wyrtki Jet contributed substantial cooling while during the second event in December 2004-January 2005 vertical processes, most likely related to entrainment mixing, were pronounced. Heavy rainfall at the mooring location during the first event may have contributed to the formation of a 30–40 m thick barrier layer that limited turbulent vertical transfers between the mixed layer and the thermocline. There was no barrier layer present during the second event, which presumably allowed for much freer vertical exchanges.

[1] Microstructure and fine-scale measurements collected in the central Bay of Biscay during the MOUTON experiment are analyzed to investigate the dynamics of internal waves and associated mixing. Large amplitude internal tides (ITs), that excite internal solitary waves (ISWs) in the thermocline, are observed. ITs are dominated by modes 3 and 4, while ISWs projects on mode-1 that is trapped in the thermocline. Therein, ITs generate a persistent narrow shear band, which is strongly correlated with the enhanced dissipation rate in the thermocline. This strong dissipation rate is further reinforced in presence of ISWs. Dissipation rates during the period without ISWs largely agree with the MacKinnon-Gregg scaling proposed for internal wave fields dominated by a low frequency mode, while they show poor agreement with the Gregg-Henyey parameterization valid for internal wave fields close to the GM model. The agreement with the MacKinnon-Gregg scaling is consistent with the fact that turbulent mixing is here driven by the low-frequency internal tidal shear.

[1] Dust particles in the approximate mass range of 10^–22 < m < 10^–20 kg produced near the Sun, due to collisions and breakup of larger interplanetary dust particles, have been shown to become entrained in the solar wind plasma flow. When these, so called nano-dust particles (NDP), impact a spacecraft, they have been suggested to produce sufficiently large plasma clouds to cause a detectable signal in the onboard electric antennas. NDPs have been identified on the twin Stereo spacecraft, and the observed intermittent nature of their fluxes were suggested to represent the stochastic nature of their sources near the Sun. Here we show that even if the generation of NDPs remains a constant in time, their detectability near the ecliptic plane becomes intermittent due their interaction with the interplanetary magnetic fields.

[1] Observations of the Atlantic Meridional Overturning Circulation (AMOC) show that it varies on all time scales. Here we isolate the contribution of eddies to AMOC variability using an eddy-permitting model of the North Atlantic driven by climatological and steady forcing. The eddy-induced AMOC variability is found to be ubiquitous and significant at all latitudes, with a magnitude comparable to the seasonal cycle in the subtropics. Furthermore, the eddy-induced AMOC variability is manifested not onlyat high frequencies, but also at interannual and longer time scales. These results imply that a significant fraction of the AMOC variability is inherently unpredictable at seasonal to interannual time scales.

[1] All climate models predict a freshening of the North Atlantic at high latitude that may induce an abrupt change of the Atlantic Meridional Overturning Circulation (hereafter AMOC) if it resides in the bistable regime, where both a strong and a weak state coexist. The latter remains uncertain as there is no consensus among observations and ocean reanalyses, where the AMOC is bistable, vs most climate models that reproduce a mono-stable strong AMOC. A series of four hindcast simulations of the global ocean at 1/12º resolution, which is presently unique, is used to diagnose freshwater transport by the AMOC in the South Atlantic, an indicator of AMOC bistability. In all simulations, the AMOC resides in the bistable regime: it exports freshwater southward in the South Atlantic, implying a positive salt advection feedback that would act to amplify a decreasing trend in subarctic deep water formation as projected in climate scenarios.

[1] Sea level rise (SLR) is an inescapable consequence of increasing greenhouse gas concentrations, with potentially harmful effects on human populations in coastal and island regions. Observational evidence indicates that global sea level has risen in the 20^th century, and climate models project an acceleration of this trend in the coming decades. Here we analyze rates of future SLR on regional scales in a 40-member ensemble of climate change projections with the Community Climate System Model Version 3. This unique ensemble allows us to assess uncertainty in the magnitude of 21^st century SLR due to internal climate variability alone. We find that simulated regional SLR at mid-century can vary by a factor of two depending on location, with the North Atlantic and Pacific showing the greatest range. This uncertainty in regional SLR results primarily from internal variations in the wind-driven and buoyancy-driven ocean circulations.

[1] A 2–3 day periodicity observed in Jupiter's magnetosphere (superposed on the giant planet's 9.5 hour rotation rate) has been associated with a characteristic mass-loading/unloading period at Jupiter. We follow a method derived by Kronberg et al., [2007] and find, consistent with their results that this period is most likely to fall between 1.5 and 3.9 days. Assuming the same process operates at Saturn we argue, based on equivalent scales at the two planets, that its period should be 4 to 6 times faster at Saturn, and therefore display a period of 8 to 18 hours. Applying the method of Kronberg et al. for the mass loading source rates estimated by Smith et al. [2010] based on data from the third and fifth Cassini-Enceladus encounters, we estimate that the expected magnetospheric refresh rate varies from 8 to 31 hours, a range that includes Saturn's rotation rate of ~10.8 hours. The magnetospheric period we describe is proportional to the total mass loading rate in the system. The period is, therefore, faster: 1) for increased outgassing from Enceladus, 2) near Saturn solstice (when the highest proportion of the rings is illuminated) and 3) near solar maximum when ionization by solar photons maximises. We do not claim to explain the few percent jitter in period derived from Saturn Kilometric Radiation with this model, nor do we address the observed difference in period observed in the North and South hemispheres.

[1] The challenge of understanding how localised deformation modifies fluid flow in porous rock is addressed. New approaches are presented, based on neutron radiography and digital image analyses, to track fluid flow in rock specimens and to calculateflow velocity fields providing local flow measurements. The results show that neutron radiography, backed-up by appropriate image analysis, is a very powerful tool in this context, being far more sensitive to the fluids in the rock than x-ray radiography. Analysis of neutron radiography images of water imbibition into a laboratory-deformed sandstone specimen has provided new measurements of local fluid flow velocities within a shear band, indicating that flow is faster and water storage is higher in the band (attributed to higher capillary forces associated with damage).

[1] The solar wind electron distribution is observed near and within 1 AU to consist of three components: a thermal core, and a suprathermal halo and strahl. The former two components are isotropic, while the strahl is field-aligned and flows outward along the interplanetary magnetic field. The evolution of solar wind electrons with heliocentric distance is poorly understood; although the halo is thought to be formed through pitch angle scattering of the strahl, the responsible physical process hasn’t been conclusively identified. Measurements of solar wind electrons throughout the heliosphere are required to solve this problem. We present the first observations of the suprathermal components of the solar wind electron distribution made outside5 AU. We find indications of a strahl component narrower than predicted by extrapolating observations and models of electrons in the inner heliosphere, suggesting the rate of electron pitch angle scattering in the solar wind can decrease with increasing heliocentric distance.

[1] The Kanto seismic corridor surrounding Tokyo has hosted 4–5 M ≥ 7 earthquakes in the past 400 years. Immediately after the Tohoku earthquake, the seismicity rate in the corridor jumped ten-fold, while the rate of normal focal mechanisms dropped in half. The seismicity rate decayed for 6–12 months, after which it steadied at three times the pre-Tohoku rate. The seismicity rate jump and decay to a new rate, as well as the focal mechanism change, can be explained by the static stress imparted by the Tohoku rupture and postseismic creep to Kanto faults. We therefore fit the seismicity observations to a rate/state Coulomb model, which we use to forecast the time-dependent probability of large earthquakes in the Kanto seismic corridor. We estimate a 17% probability of a M ≥ 7.0 shock over the 5-year prospective period 11 March 2013 to 10 March 2018, two-and-a-half times the probability had the Tohoku earthquake not struck.

[1] In the paper “Changes in Arctic sea ice result in increasing light transmittance and absorption” by M. Nicolaus et al. (Geophysical Research Letters, 39, 24, doi:10.1029/2012GL053738, 2012) the presented data on solar surface irradiance are erroneous.

[1] Four repeat hydrographic sections across the eastern Weddell gyre at 30ºE reveal a warming (by ~0.1 °C) and lightening (by ~0.02-0.03 kg m^-3) of the Antarctic Bottom Water (AABW) entering the gyre from the Indian sector of the Southern Ocean between the mid-1990s and late 2000s.Historical hydrographic and altimetric measurements in the region suggest that the most likely explanation for the change is increased entrainment of warmer mid-depth Circumpolar Deep Water by cascading shelf water plumes close to Cape Darnley, where the Indian-sourced AABW entering the Weddell gyre from the east is ventilated. This change in entrainment is associated with a concurrent southward shift of the Antarctic Circumpolar Current's (ACC) southern boundary in the region. This mechanism of AABW warming may affect wherever the ACC flows close to Antarctica.

[1] The cause of seismic anisotropy exhibiting trench parallel fast directions in subduction systems has been the subject of significant recent research. We provide new constraints on the contributions of hydrous phases to seismic anisotropy from an unusually well localized region of trench parallel fast directions in Rayleigh wave phase velocities near the Cascade arc at 45 to 66 second periods. We constrain the location of the anisotropic material to within or directly above the oceanic plate, using the depth sensitivity of Rayleigh waves as a function of frequency and the accurate slab imaging available for Cascadia from scattered wave studies. We infer that the likely source of trench-parallel anisotropy is either a thin layer of sheared hydrous material directly above the slab or hydrated outer-rise faults in the upper part of the subducting plate. Similar contributions to trench parallel anisotropy from hydrous phases are likely stronger in other subduction zones.

[1] April–May tornado day likelihood from 1990–2011 was calculated for the central U.S. for phases of the Madden-Julian Oscillation (MJO). An April tornado day was found more likely during MJO phases 6 and 8 and less likely during phases3, 4, and 7. A May tornado day was found more likely during phases 5 and 8 and less likely in phases 2 and 3. During phases with above-normal tornado day likelihoods, positive anomalies of convective available potential energy, bulk vertical wind shear, and storm-relative helicity were found in the central U.S. Negative anomalies were found during phases with below-normal tornado day likelihoods. Anomalies of such environmental parameters were connected to the MJO via variability in tropospheric circulation. These results provide an important starting point for extended-range prediction of U.S. tornado activity.

[1] Time-variable gravity data from the Gravity Recovery And Climate Experiment (GRACE) mission have been available since 2002 to estimate the mass balance of the Greenland and Antarctic Ice Sheets. We analyze current progress and uncertainties in GRACE estimates of ice sheet mass balance. We discuss the impacts of errors associated with spherical harmonic truncation, spatial averaging, temporal sampling, and leakage from other time-dependent signals (e.g. Glacial Isostatic Adjustment (GIA)). The largest sources of error for Antarctica are the GIA correction, the omission of l = 1 terms, non-tidal changes in ocean mass, and measurement errors. For Greenland, the errors come mostly from the uncertainty in the scaling factor. Using Release 5.0 (RL05) GRACE fields for Jan 2003 through Nov 2012, we find a mass change of −258 ± 41 Gt/yr for Greenland, with an acceleration of −31 ± 6 Gt/yr², and a loss that migrated clockwise around the ice sheet margin to progressively affect the entire periphery. For Antarctica, we report changes of −83 ± 49 and −147 ± 80 Gt/yr for two GIA models, with an acceleration of −12 ± 9 Gt/yr² and a dominance from the southeast pacific sector of West Antarctica and the Antarctic Peninsula.

[1] During an 8-day drift in July-August 2012 in the Nansen Basin, all components of the energy budget of melting first-year sea ice were observed. Absorption of solar radiation by the ice and ponds was the largecprst source of energy to the ice at almost all times during the drift. However, oceanic heat flux also provided significant heating and dominated during one wind event. Longwave fluxes provided a relatively small cooling effect, and atmospheric heat fluxes were negligible. The aggregate scale albedo of this younger, thinner ice was significantly lower than at SHEBA, and the transmittance was significantly higher here, despite similar pond and open water fractions. The oceanic heat flux was only half of the solar flux through the ice to thewater, producing warm water near the surface that might delay ice growth in autumn, an important effect of the transition to thinner first-year ice in the high Arctic.

[1] The potential effect on surface water pH of emissions of SO_X and NO_X from global ship routes is assessed. The results indicate that regional pH reductions of the same order of magnitude as the CO₂-driven acidification can occur in heavily trafficked waters. These findings have important consequences for ocean chemistry, since the sulfuric and nitric acids formed are strong acids in contrast to the weak carbonic acid formed by dissolution of CO₂. Our results also provide background for discussion of expanded controls to mitigate acidification due to these shipping emissions.

[1] Indian Summer Monsoon (ISM) is mainly characterized by seasonal wind reversal in low level jet stream and tropical easterly jet (TEJ) among several other elements of monsoon systems. TEJ is observed in general between 100 and 150 hPa during June-September over the Indian region and its strength is directly related to the monsoon rainfall. In the context of changing climate, large reduction in its extent and weakening of its strength were reported. Using high resolution measurements, we report here the observation of a sharp strengthening of the TEJ during the recent warmest decade (2001–2010), reaching its 1970's value. We also show that this change is reflected in the tropical cyclone systems and finally on the precipitation patterns over the Indian region as they are interlinked. We attribute this unusual change partly to the change in the circulation due to the tropospheric warming and lower stratospheric ozone recovery.

[1] The sub-grid scale surface momentum transport, which plays an important role in determining the exchange between the atmosphere and the underlying surface, is often parameterized in terms of the surface mean wind speed via drag coefficient (C_D), a parameter that needs to be determined externally often through the Monin-Obukhov Similarity theory (MOS). However, some characteristics of C_D derived from observations for overland conditions, particularly, the substantial increase of C_D with a decrease in wind speed in low wind conditions, cannot be explained by MOS. This issue is investigated using data collected by a portable meteorological tower. By analyzing the turbulent kinetic energy budget, a novel parameterization framework for momentum fluxes is proposed. The new parameterization not only appropriately describes the observed variation of C_D but also can be simplified to MOS with certain assumptions. Moreover, the effect of stability, which traditionally has to be determined empirically, can now be determined internally within the new framework.

[1] A comprehensive General Circulation Model (GCM) is used to estimate the climate impact of aviation emissions of black carbon (BC) and sulfate (SO⁴) aerosols. Aviation BC is found not to exert significant radiative forcing impacts, when BC nucleating efficiencies in line with observations are used. Sulfate emissions from aircraft are found to alter liquid clouds at altitudes below emission (~200 hPa); contributing to shortwave cloud brightening through enhanced liquid water path and drop number concentration in major flight corridors, particularly in the N. Atlantic. Global averaged sulfate direct and indirect effects on liquid clouds of 46 mWm⁻² are larger than the warming effect of aviation induced cloudiness of 16 mWm⁻². The net result of including contrail cirrus and aerosol effects is a global averaged cooling of −21 ± 11 mWm⁻². These aerosol forcings should be considered with contrails in evaluating the total global impact of aviation on climate.

[1] On Europa, the mechanism by which contractional strains are accommodated remains a mystery. Subtle folds have been observed in the polar regions, but if folding is a dominant accommodation mechanism, ubiquitous large-amplitude folds might be expected across Europa's surface. Here we use finite element modeling to show that fold growth rates are a strong function of surface temperature: warm temperatures result in lower rates, cold temperatures result in higher rates. Combining diurnally averaged Europan surface temperatures derived from Galileo photopolarimeter-radiometer data and new numerical simulations, we show that forming moderate-amplitude folds requires roughly twice the contraction, or shortening, in Europa's equatorial latitudes, relative to polar latitudes. Relatively large contractional strains in Europa's equatorial and mid-latitudes can therefore be accommodated primarily through passive shortening without producing obvious folds. Lithospheric folding and/or passive shortening therefore remain plausible mechanisms for strain accommodation on Europa.

[1] At Santorini, active normal faulting controls the emission of volcanic products. Such geometry has implication on seismic activity around the plumbing system during unrest. Static Coulomb stress changes induced by the 2011-2012 inflation within a preexisting NW-SE extensional regional stress field, compatible with fault geometry, increased by more than 0.5 MPa in an ellipsoid-shaped zone beneath the Minoan caldera where almost all earthquakes (96%) have occurred since beginning of unrest. Magmatic processes perturb the regional stress in the caldera where strike-slip rather than normal faulting along NE-SW striking planes are expected. The inflation may have also promoted more distant moderate earthquakes on neighboring faults as the M > 5 January 2012, south of Christiania. Santorini belongs to a set of en echelon NE-SW striking rifts (Milos, Nysiros) oblique to the Aegean arc that may have initiated in the Quaternary due to propagation of the North Anatolian fault into the Southern Aegean Sea.

[1] Global arc magmatism is sustained by a continuous fluid flux that is returned to the mantle in subduction zones. Despite considerable advances in simulations of melting processes, models of arc magmatism remain incompletely tested against erupted products. Here, we show that a suite of primitive volcanic rocks from across the southern Chilean arc preserves the signature of a systematic down-slab gradient in fluid chemistry. The chemical gradient is consistent with predictions from modelling, geothermometry and experiments. We infer that increasing slab-surface temperatures cause the sub-arc slab flux to become less water-rich and increasingly dominated by hydrous melts over a distance of a few kilometres behind the arc front. This change exerts a first-order control on magma chemistry, and implies discrete melt-transport pathways through subduction zones. Our results replicate patterns in other arcs, implying common sub-arc slab-surface temperature ranges in thermally diverse subduction zones.

[1] The quasi-biennial oscillation (QBO), El Niño Southern Oscillation (ENSO), and upwelling in the tropical branch of the Brewer-Dobson circulation (BDC) impact tropical tropopause layer (TTL, 14–19 km) temperature (T) and relative humidity (RH), and thus it is likely that they also affect the TTL cloud distribution. Satellite data reveal extreme interannual variability in the zonal-mean TTL cloud occurrence frequency (CF) in the deep tropics (10°S – 10°N). This zonal-mean interannual variability is related to the QBO and BDC, with a relatively minor role for ENSO. However, over the whole tropics

[2] (30°S – 30°N), the dominant mode of variability in the longitudinally resolved CF field is an ENSO-related dipole pattern of positive and negative anomalies centered over the Pacific that mimics the RH/T fields. The ENSO effects largely cancel in the zonal-mean, although El Niño is weakly associated with enhanced zonal-mean cloudiness in the uppermost TTL over the short satellite record.

[1] The seismic structure of the continent-ocean transition (COT) at magma-poor rifted margins can explain geological processes leading to continental breakup. At the Newfoundland-Iberia rift, compressional seismic velocity (V_p) is interpreted with multichannel seismic reflections (MCS) and drilling results to document continental crustal stretching and thinning, exhumation of the mantle, and incipient seafloor-spreading. However, V_p cannot uniquely constrain COT geology. We present an updated 2-D model for V_p and a new shear-wave velocity model (V_s) for SCREECH Line 2 on the Newfoundland margin using MCS and coincident ocean-bottom seismometer (OBS) refraction data. In shallow COT basement we find V_p/ V_s ratios average 1.77, which is normally too high for upper continental crust and too low for serpentinized mantle. This observation can be explained by stretching of a mafic middle and/or lower continental crust into the COT. We further support the presence of hydrated mantle peridotites at depth during rifting.

[1] We have numerically simulated dynamic ruptures along a “slip-weakening” megathrust fault with a subducted seamount of realistic geometry, demonstrating that seamounts can act as a barrier to earthquake ruptures. Such barrier effect is calculated to be stronger for increased seamount normal stress relative to the ambient level, for larger seamount height-to-width ratio, and for shorter seamount-to-nucleation distance. As the seamount height increases from 0 to 40% of its basal width, the required increase in the effective normal stress on the seamount to stop ruptures drops by as much as ~20%.We further demonstrate that when a seamount is subducted adjacent to the earthquake nucleation zone, coseismic ruptures can be stopped even if the seamount has a lower effective normal stress than the ambient level. These results indicate that subducted seamounts may stop earthquake ruptures for a wide range of seamount normal stress conditions, including the case of the thrust fault being lubricated by seamount-top fluid-rich sediments, as suggested from observations in the Japan and SundaTrenches.

[1] The tidally driven vertical diffusivity in the abyssal ocean during the early Eocene (55 Ma) is investigated using an established tidal model. A weak tide is predicted in the Eocene ocean, except in the Pacific. Consequently, the integrated global tidal dissipation rates are a mere 1.44TW, of which 40% dissipate in the Pacific. However, due to a stronger abyssal vertical stratification the predicted Eocene vertical diffusivities are consistently larger than at present. The results support the hypothesis that altered tidal dissipation may play a role in explaining the maintenance of past climate regimes, especially the anomalously warm temperatures in the southwest Pacific in the Eocene, and the low dissipation rates may be important for lunar evolution history.

[1] The impact of variations of the Walker cell on the ocean carbon cycle is assessed using a coupled climate model. Idealized wind perturbations are investigated, with the trade winds increased/decreased by 10, 20, and 30%. A global-mean reduction in oceanic carbon storage is found for increased equatorial easterlies, while moderately decreased trade winds give increased uptake. There is a non-linear response to weakened tropical winds due to Pacific Ocean biological pump changes; with reduced nutrient upwelling resulting in decreased biological activity and remineralization in the deep ocean. This partially offsets the increased carbon uptake due to weaker trade winds. The overall change in net carbon storage reaches -26.2 PgC (12 ppm) in the 30% increase case and 4.2 PgC (-2 ppm) in the 20% decrease cases. Regional DIC changes reach -3.3 mmol m^-3 (2.1 mmol m^-3) in the 10% decrease (increase) case. Gradually increasing wind perturbations give a similar pattern of DIC response to the full equilibrated solution.

[1] Atmospheric thermal tides are global oscillations in atmospheric fields that are sub-harmonics of a solar day. While atmospheric tides on Earth are mainly relevant in the upper atmosphere, on Mars they dominate temperature variations and winds throughout the atmosphere. Observations and model simulations to date have suggested that the migrating diurnal tide is the predominant mode in the martian atmosphere, and that the semi-diurnal tide is only relevant in the tropical middle atmosphere during conditions of high dust loading. New comprehensive observations by the Mars Climate Sounder in a geometry that allows coverage of multiple local times show that the semi-diurnal tide is a dominant response of the martian atmosphere throughout the martian year. The maximum semi-diurnal amplitude of ∼ 16 K is found at southern winter high latitudes, which makes it the largest tidal amplitude observed in the martian middle atmosphere outside of dust storm conditions. The semi-diurnal tide can be successfully modeled due to recent advances of Mars General Circulation Models (MGCMs) that include the radiatively active treatment of water ice clouds. Tidal forcing occurs through absorption of radiation by aerosols and points to the vertical structure of dust and clouds and their radiative effects as being essential for our understanding of the thermal structure and the general circulation of the martian atmosphere. As with terrestrial GCMs trying to quantify mechanisms affecting climate, future Mars modeling efforts will require microphysical schemes to control aerosol distributions, and vertically and temporally resolved measurements of temperature and aerosols will be essential for their validation.

[1] Paleofire events obtained from the statistical treatment of sedimentary charcoal records rely on a number of assumptions and user's choices, increasing the uncertainty of reconstructions. Among the assumptions made when analyzing charcoal series is the choice of a filtering method for raw Charcoal Accumulation Rate (CHAR_raw). As there is no ultimate CHAR_raw filtering method, we propose an ensemble-member approach to reconstruct fire events. We modified the commonly-used procedure by including a routine replicating the analysis of a charcoal record using custom smoothing parameters. Dates of robust fire events, uncertainties in fire-return intervals and fire frequencies are derived from members’ distributions. An application of the method is used to quantify uncertainties due to data treatment in two CHAR_raw sequences from two different biomes, subalpine and boreal.

[1] When the interplanetary magnetic field (IMF) is dawnward or duskward, magnetic merging between the IMF and the geomagnetic field occurs near the cusp on the dayside flanks of the magnetosphere. During these intervals, flow channels in the ionosphere with velocities in excess of 2 km/s have been observed, which can deposit large amounts of energy into the high-latitude thermosphere. In this study, we analyze an interval on 5 April 2010 where there was a strong dawnward impulse in the IMF, followed by a gradual decay in IMF magnitude at constant clock angle. Data from the Sondrestrom incoherent scatter radar and the DMSP spacecraft were used to investigate ionospheric convection during this interval, and data from the Active Magnetospheric and Planetary Electrodynamics Response Experiment (AMPERE) were used to investigate the associated Field-Aligned Current (FAC) system. Additionally, data from AMPERE were used to investigate the time response of the dawn-side FAC pair. We find there is a delay of approximately 1.25 hours between the arrival of the dawnward IMF impulse at the magnetopause and strength of the dawnward FAC pair, which is comparable to substorm growth and expansion time scales under southward IMF. Additionally, we find at the time of the peak FAC, there is evidence of a reconfiguring four-sheet FAC system in the morning local time sector of the ionosphere. Additionally, we find an inverse correlation between the dawn FAC strength and both the solar wind Alfvénic Mach number and the SYM-H index. No statistically significant correlation between the FAC strength and the solar wind dynamic pressure was found.

[1] The hydrographic dataset of the German Atlantic Expedition (GAE) 1925–27 is compared with the contemporary profiling float and ship-based hydrography to reveal full-depth changes in the Atlantic Ocean between 19 ^oN and 64 ^oS. The volume-mean warming over the last 80 years amounts to 0.119 ± 0.067 °C, accompanied by an increase in salinity of 0.014 ± 0.010. A clear vertical structure of these changes is observed: on average the ocean has warmed by 0.272 ± 0.093 °C and became saltier by 0.030 ± 0.014 down to about 2000 m, but cooled and freshened slightly in the deeper layers. These changes can be traced throughout the whole hydrographic survey between 19 ^oN and 55 ^oS, indicating the basin-wide character of the observed changes on a centennial time-scale. The observed warming is consistent with climate model simulations over the 20^th century, suggesting an attribution to anthropogenic forcing. Comparison with the pre-GAE cruises reveals no discernable warming between 1870 s and 1906/11.

[1] Total electron content (TEC) measured by Global Positioning System (GPS) receivers in the United States Great Plains is examined for three nights with large thunderstorms and for one night with little thunderstorm activity. The GPS TEC data are fit with a polynomial and the variations are estimated by subtracting this fit from the data. We found that anomalous TEC variations are closely associated in time and space to the large underlying thunderstorms. The largest storm-related TEC variation is observed to be ~1.4 TECU over a typical nighttime background value of several TECUs. The variations near the storm appear to have more high frequency content than those away from the storm, with periods of minutes to tens of minutes. No detectable localized TEC variation is observed for the thunderstorm-quiet night.

[1] Human influence on atmospheric sea level pressure (SLP) has previously been detected globally, but the contributions of greenhouse gas, aerosol and ozone changes to the observed trends have not been separately identified. We use simulations from eight climate models to show that greenhouse gas, aerosol and ozone changes each drive distinct seasonal and geographical patterns of trends, which are separately detectable in observed seasonal SLP trends over the 1951–2011 period. This detection is driven by significant low-latitude SLP responses to greenhouse gas, aerosol and ozone changes, as well as the more frequently-studied high latitude responses. These results aid in understanding past atmospheric circulation changes, and have potential to improve projections of future circulation changes.

[1] We measured the escape of methane-containing gas bubbles to the water table in two microhabitats (muddy hollows and Sphagnum-plus-sedge lawns) in a raised bog in West Wales, typical of many northern peatlands. Our study was unusual in its degree of replication (14 gas traps in each microhabitat). Seasonally-integrated bubble loss of CH₄ to the water table did not differ significantly between microhabitats. After applying an oxidation correction to give CH₄ fluxes to the atmosphere, the microhabitats still did not differ. Our results suggest that ebullition is an important mechanism of CH₄ loss to the atmosphere, with mean summer rates of 11.7 mg CH₄ m^-2 day^-1 (muddy hollows) and 6.8 mg CH₄ m^-2 day^-1 (Sphagnum-plus-sedge lawns). Our data show that the process is spatially and temporally very variable, and that the small sample sizes of many studies (e.g., n = 5) may lead to considerable errors in flux estimation.

[1] In this paper, we demonstrate a global-scale southward shift of the tropical rain belt during the latter half of the 20^th century in observations and global climate models (GCMs). In rain gauge data, the southward shift maximizes in the 1980s, and is associated with signals in Africa, Asia and South America. A southward shift exists at a similar time in nearly all CMIP3 and CMIP5 historical simulations, and occurs on both land and ocean, although in most models the shifts are significantly less than in observations. Utilizing a theoretical framework based on atmospheric energetics, we perform an attribution of the zonal mean southward shift of precipitation across a large suite of CMIP3 and CMIP5 GCMs. Our results suggest that anthropogenic aerosol cooling of the Northern Hemisphere is the primary cause of the consistent southward shift across GCMs, although other processes affecting the atmospheric energy budget also contribute to the model-to-model spread.

[1] The aerosol direct radiative effects (DRE) in the ultraviolet, shortwave and longwave range due to an unusual dust storm during March 21, 2012 have been quantified from surface measurements of AOD and radiation fluxes at Delhi, a western Indo Gangetic Plain station. The intrusion of dust over Delhi caused an increase in daily average AOD at 500 nm from 0.6 to 0.8 with a corresponding decrease in Angstrom Exponent from 0.4 to sub-zero value. The dust severely affected the incoming solar radiation flux in the UV, shortwave and longwave region. The DRE at surface in the UV and shortwave decreased from -4.6 to -5.9 Wm^-2 and from -68 to -86 Wm^-2 respectively, while the longwave DRE increased from 27 to 45 Wm^-2.

[1] Drought is typically associated with a lack of precipitation, whereas the contribution of evapotranspiration and runoff to drought evolution is not well understood. Here, we use unique long-term observations made in four headwater catchments in Central and Western Europe to reconstruct storage anomalies and study the drivers of storage anomaly evolution during drought. We provide observational evidence for the ‘drought-paradox’ in that region: a consistent and significant increase in evapotranspiration during drought episodes which acts to amplify the storage anomalies. In contrast, decreases in runoff act to limit storage anomalies. Our findings stress the need for the correct representation of evapotranspiration and runoff processes in drought indices.

[1] The vertical transport of large volumes of silicic magma, which drives volcanic eruptions and the long-term compositional evolution of the continental crust, is a highly debated problem. In recent years, dyking has been favoured as the main ascent mechanism but the structural connection between a distributed configuration of melt-filled pores in the source region and shallow magma reservoirs remains unsolved. In the Central Andes, inversion of a new high-resolution Bouguer Anomaly over the Altiplano-Puna Magma Body (APMB), reveals ~15 km-wide, vertically-elongated, low-density, 3D structures rooted at the top of the APMB at 20 km depth. We integrate our gravity inversion with the available geophysical, geological and petrological observations, and in agreement with petrological/mechanical considerations propose that, in this region of the Andes, partially molten granitic bodies ascend diapirically through the hot ductile mid-upper crust.

[1] The relative importance of tropical SST anomalies to the dominant variability of East Asian Summer Monsoon (EASM) Circulation is investigated using an atmospheric GCM and a linear inverse model. It is found that the cooling over the central tropical Pacific is crucial in developing and maintaining the summertime northwest Pacific anticyclones, associated with the EASM precipitation. In this regard, the previously suggested El Niño event in the preceding winter and accompanying tropical Indian Ocean warming alone may not be enough to predict the strength of EASM circulation. Instead, monitoring and predicting the evolution of sea surface temperature anomalies in the central tropical Pacific, especially in spring to summer, may greatly improve the prediction of EASM circulation.

[1] We present direct, global observations of longitudinally averaged CHAMP zonal winds gathered between 2003–2007. A diurnal variation dominates the global zonal wind. Westward flows are observed from the early morning through afternoon hours, while eastward flows peak in the evening. A semidiurnal harmonic is also present, with magnitudes that are approximately one third of the diurnal harmonic. The time mean wind indicates westward winds over much of the globe, with weak superrotation (+E, or eastward winds) that is symmetric about the equator during equinox, and confined to the winter hemisphere at solstice. Diurnal and time-mean CHAMP winds agree fairly well with the Whole Atmosphere Model. Some differences are observed in the semidiurnal and higher-order tidal winds, that underscore the challenges of modeling the sources, sinks and mean wind effects upon tides between the surface and 400 km.

[1] Intense electromagnetic ion cyclotron (EMIC) waves are observed within plasmaspheric plumes during geomagnetic storms and are believed to be a significant driver of loss of both ring current protons and radiation belt electrons. In this study we use ray tracing together with path-integrated linear growth calculations to analyze the amplification and propagation of EMIC waves within cold plasma density irregularities characteristic of the plasmaspheric plume. All waves are launched at the equator in the range of L = 5 to 7, and wave amplification is analyzed as a function of frequency and initial wave normal angle. These results are compared to a baseline case without irregularities, which show that guiding is possible for irregularity sizes on the order of the EMIC wavelength. Results suggest that typical structures with density levels above and below the average value can result in both areas of increased as well as suppressed wave activity.

[1] From long-period magnetotelluric data across the Gawler Craton, we obtain a three-dimensional resistivity image of the lithosphere and provide constraints on tectonothermal events dating back to the Proterozoic. Contrary to common observations of Archean cratons displaying high electrical resistivity in the mantle lithosphere, the magnetotelluric data show low resistivity of around 10 Ωm at 80 km depth underneath the 1595 Ma Gawler Range Volcanics, a silicic Large Igneous Province. The resistivity distribution appears to be a signature of plume-modified orogenesis with low-degree partial melting at the base of the lithosphere in a back-arc setting. The enhanced conductivity is explained through higher hydrogen and iron content in the crystal lattice and also along the grain boundaries of the mantle constituting minerals. Older, arc-related magmatism to the south-west across 1620-1610 Ma St. Peter Suite does not display enhanced conductivity and suggests a depleted mantle lithosphere. The data show that Yellowstone-type mantle plume analogues are preserved through time and still display an elevated electrical signature in the lithosphere today.

[1] Using a numerical model we show that the surf zone of embayed beaches systematically flushes out more floating material (simulated using passive tracers) than on open beaches, with most exits occurring through the headland rips. For obliquely incident waves, a headland rip acts as a persistent conduit for transporting floating material out of the surf zone and into the inner shelf region. Wave angle and embayment size determine which headland rip (upwave or downwave) flushes out more the surf zone material. For narrow embayed beaches passive drifters exit the surf zone through the upwave headland rip. For wider embayed beaches, the longshore current has enough room to develop and is further deflected against the downwave headland where most drifters exit the surf zone. Our results indicate that wave-exposed rugged coasts strongly enhance exchange of floating matter (e.g., pollutants and nutrients) at the ocean/continent interface.

[1] The Tokyo metropolitan area, underlain by Neogene and Quaternary sediments more than 5 km thick, is currently deformed by blind thrusts that could generate hazardous earthquakes. However, their little geomorphic expression and dense urbanization make understanding of folds produced above them and recent deformation highly elusive. Here we show subsurface geometries of several active blind thrusts beneath this highly urbanized area, based on tectonic landforms, high-resolution seismic reflection data, and Quaternary stratigraphy. Deep seismic reflection profiles corroborate the notion that steeply dipping blind thrusts are reactivated normal faults originally formed by middle Miocene extensional tectonics. Despite very slow (less than 0.1 mm/yr) late Quaternary slip rates, our work suggests the presence of previously unrecognized faults that pose seismic hazards to Tokyo and outlying communities, highlighting the need for additional information to define recent slip rates, magnitude and recurrence of past earthquakes on them.

[1] Antarctic Bottom Water (AABW) is formed in a few locations around the Antarctic continent, each source with distinct temperature and salinity. After formation, the different AABW varieties cross the Southern Ocean and flow into the subtropical abyssal basins. It is shown here, using the analysis of Lagrangian trajectories within the Southern Ocean State Estimate (SOSE) model, that the pathways of the different sources of AABW have to a large extent amalgamated into one pathway by the time it reaches 31°S in the deep subtropical basins. The Antarctic Circumpolar Current appears to play an important role in the amalgamation, as 70% of the AABW completes at least one circumpolar loop before reaching the subtropical basins. This amalgamation of AABW pathways suggests that on decadal to centennial time scales, changes to properties and formation rates in any of the AABW source regions will be conveyed to all three subtropical abyssal basins.

[1] We constructed a three-dimensional conceptual model of a geothermal system on the Caribbean island of Montserrat. The model was generated using magnetotelluric resistivity data, earthquake hypocenter data and a three-dimensional P-wave velocity model all plotted using a shared geographical reference. The results of the study suggest a high-temperature fracture controlled geothermal system at the intersection of two faults in the SW of the island. We also present a ‘prospectivity index’ map that represents a proxy of the spatial variation in harvestable heat flux at 1500 m depth. The index is the product of relative permeability around modeled faults and a proxy for the subsurface temperature calculated using P-wave velocity anomalies.

[1] Natural climate variability will continue to be an important aspect of future regional climate even in the midst of long-term secular changes. Consequently, the ability of climate models to simulate major natural modes of variability and their teleconnections provides important context for the interpretation and use of climate-change projections. Comparisons reported here indicate that the CMIP5 generation of global climate models shows significant improvements in simulations of key Pacific climate mode and their teleconnections to North America compared to earlier CMIP3 simulations. The performance of fourteen models with simulations in both the CMIP3 and CMIP5 archives are assessed using singular value decomposition analysis of simulated and observed winter Pacific sea-surface temperatures (SSTs) and concurrent precipitation over the contiguous United States and northwestern Mexico. Most of the models reproduce basic features of the key natural mode and their teleconnections, albeit with notable regional deviations from observations in both SST and precipitation. Increasing horizontal resolution in the CMIP5 simulations is an important, but not a necessary factor in the improvement from CMIP3 to CMIP5.

[1] Rock varnish from 14.6–13.2 ka recessional shorelines of late glacial Lake Lisan and fan delta surfaces between 280 and 365 m bmsl (meters below mean sea level) along the western margins of the Dead Sea contains replicable layering patterns, characterized by a low Mn and Ba orange/yellow surface layer and a high Mn and Ba dark basal layer. The deposition of the dark basal layers immediately after the lake recession represents a wet period coinciding with the Younger Dryas (YD) cooling (12.9–11.6 ka), manifesting the influence of mid-latitude westerly winds in the eastern Mediterranean-central Levant (EM-CL). In contrast, varnish from the distal base of fan deltas contains only orange/yellow surface layers, diagnostic of the Holocene relatively dry climate. The absence of the dark basal layers in the varnish further indicates an YD high stand at ~365 m bmsl and a lake level rise of at least 100 m from its Bølling-Ållerød low stand. This rise stands in contrast to the abrupt drop of the lake level during the Heinrich (H1) cold event, illustrating the opposite response of the EM-CL climate to changes in the North Atlantic climate. The YD wet event most likely reflects a southward shift of the Atlantic meridional overturning circulation-modulated mid-latitude westerly wind belt in the EM-CL region.

[1] Hyperpycnal gravity currents rapidly transport sediment across-shore from rivers to the continental shelf and deep sea. Although these geophysical processes are important sediment dispersal mechanisms, few distinct geomorphic features on the continental shelf can be attributed to hyperpycnal flows. Here we provide evidence of large depositional features derived from hyperpycnal plumes on the continental shelf of the northern Santa Barbara Channel, California, from the combination of new sonar, lidar and seismic-reflection data. These data reveal lobate fans directly offshore of the mouths of several watersheds known to produce hyperpycnal concentrations of suspended sediment. The fans occur on an upwardly concave section of the shelf where slopes decrease from 0.04 to 0.01, and the location of these fans is consistent with wave- and auto-suspending sediment gravity current theories. Thus, we provide the first documentation that the morphology of sediment deposits on the continental shelf can be dictated by river-generated hyperpycnal flows.

[1] Saharan dust affects the climate by altering the radiation balance and by depositing minerals to the Atlantic Ocean. Both are dependent on particle size. We present aircraft measurements comprising 42 profiles of size distribution (0.1 – 300 µm), representing freshly uplifted dust, regional aged dust and dust in the Saharan Air Layer (SAL) over the Canary Islands. The mean effective diameter of dust in SAL profiles is 4.5 µm smaller than that in freshly uplifted dust, whilst the vertical structure changes from a low shallow layer (0–1.5 km) to a well-mixed deep Saharan dust layer (0–5 km). Size distributions show a loss of 60 to 90% of particles larger than 30 µm 12 hours after uplift. The single scattering albedo (SSA) increases from 0.92 to 0.94 to 0.95 between fresh, aged and SAL profiles: this is enough to alter heating rates by 26%. Some fresh dust close to the surface shows SSA as low as 0.85.

[1] The North-Western Sahara Aquifer System (NWSAS), one of the world's largest groundwater systems, shows an overall piezometric decline associated with increasing withdrawals. Estimating the recharge rate in such a semiarid system is challenging but crucial for sustainable water development. In this paper, the recharge of the NWSAS is estimated using a regional water budget based on GRACE terrestrial water storage monthly records, soil moisture from the GLDAS (a land data system that assimilates hydrological information) and groundwater pumping rates. A cumulated natural recharge rate of 1.40 ± 0.90 km ³ yr ^− 1 is estimated for the two main aquifers. Our results suggest a renewal rate of about 40% which partly contradicts the premise that recharge in this area should be very low or even null. Aquifer depletion inferred from our analysis is consistent with observed piezometric head decline in the two main aquifers in the region. Annual recharge variations were also estimated and vary between 0 and 4.40 km ³ yr ^− 1 for the period 2003-2010. These values correspond to a recharge between 0 and 6.75 mm yr ^− 1 on the 650000 km ² of outcropping areas of the aquifers, which is consistent with the expected weak and sporadic recharge in this semiarid environment. These variations are also in line with annual rainfall variation with a lag time of about one year.

[1] To understand mechanisms of shortwave cloud-radiative feedback to global warming in a general circulation model (GCM), we analyzed the response of tropical clouds to uniform increase of sea surface temperature in an atmospheric GCM with two different experimental designs: a single Atmospheric Model Intercomparison Project (AMIP) run for 30 years, and a series of 10-day weather hindcasts following the Transpose AMIP II (TAMIP). Given the fast timescale of cloud processes, the hindcast ensemble can capture initial transient responses toward equilibrium obtained in the AMIP experiment, which shows a reduction of low clouds over tropical subsidence regions. The reduction of clouds occurs in the first 10 days in TAMIP when the marine boundary layer (MBL) is destabilized because of contrast between fast and slow warming in the MBL and aloft. Enhanced evaporation from the sea surface that should moisten the MBL through turbulent mixing is suppressed by a reduced surface wind speed associated with a slowdown of the Walker circulation. The sign of the low-cloud change over the subsidence regime is thus determined roughly by competition between convective drying and turbulent moistening of the MBL.

[1] Atmospheric methane (CH₄) concentration in the mid-to-upper troposphere has been retrieved using atmospheric infrared sounder (AIRS) data on NASA EOS/AQUA. By selecting the AIRS strong CH₄ absorption channels near 1306 cm^-1, severe CH₄ depletion was mapped during a stratospheric intrusion event on March 27, 2010. The areas with depleted CH₄ mixing ratio are collocated with enhanced ozone (O₃) and low tropopause height. Aircraft measurements observed the depleted CH₄ and enhanced O₃ down to 550 hPa. An estimate of the depleted CH₄ amount resulted from stratospheric intrusion is -54 to -67 Tg yr^-1. This study suggests that the AIRS and/or other thermal infrared sounders can provide an observation of CH₄ variation associated with stratospheric intrusion, a key unknown in CH₄ budget, and this dataset will be also useful for studying the stratosphere-troposphere exchange (STE).

[1] Future changes in the occurrence rates of major stratospheric warmings (MSWs) have recently been identified in Chemistry-Climate Model (CCM) simulations, but without reaching a consensus, potentially due to the competition of different forcings. We examine future variations in the occurrence rates of MSWs in transient and timeslice simulations of the ECHAM/MESSy Atmospheric Chemistry (EMAC) CCM, with a focus on the individual effect of different external factors. While no statistically significant variation is found in the decadal-mean frequency of MSWs, a shift of their timing towards midwinter is detected in the future. The strengthening of the polar vortex in early winter is explained by recovering ozone levels following the future decrease in ozone-depleting substances. In midwinter, a stronger dynamical forcing associated with changes in tropical sea surface temperatures will lead to more MSWs, through a similar mechanism that explains the stratospheric response to ENSO.

[1] Presence of graphite is one of the mechanisms to explain enhanced electrical conductivity. Because the conductivity of graphite is highly anisotropic and the connectivity of graphite depends strongly on the geometry of the crystals, the key issue is the geometry of graphite in a rock including their crystallographic orientation and the shape of graphite crystals. We explored the role of graphite on electrical conductivity in olivine-rich aggregates. To obtain well-defined results, we conducted an experimental study at high pressure and temperature conditions where graphite assumes equilibrium morphology. Olivine aggregates containing diamonds were annealed to transform diamond to graphite with nearly equilibrium morphology. Graphite formed by the transformation from diamond has thin disk-shape morphology, the plane being the highly conductive (0001) plane. The concentration of graphite exceeds the percolation threshold and electrical conductivity is significantly enhanced. Some of the observed high conductivity regions may represent regions of high concentration of graphite.

[1] For faults without sedimentary covers, there is no robust method to obtain paleoseismic data which is crucial for the prediction of future damaging earthquake events. Sudden failure along faults during earthquakes induces off-fault damage surrounding such basement faults. We showed that the Quaternary-active fault has the damage zone characterized by a fracture density that decays exponentially with distance from the fault for both healed and open microfractures. In contrast, Quaternary-inactive faults contain only healed microfracture damage zone. Cross-cutting relationships between microfractures and a minimum healing temperature of ~100 °C suggest that healed microfractures formed before, and at deeper levels, than did unhealed microfractures. The damage zone defined by open microfractures reflects the recent fault movement during exhumation, associated with erosion and regional uplift, from the maximum depth at which microfractures may remain unhealed. Microfracture analysis can therefore be used to examine the history of basement fault activity.

[1] Mauna Loa and Kilauea volcanoes, Hawaii, are thought to be coupled by pore pressure diffusion through an asthenospheric melt layer. However, abundant observations of independent activity of these volcanoes suggest a complicated relationship. Here, we analyze surface deformation data, deep seismicity and gas measurements, to reveal strong coupling of these volcanoes between 2003 and 2008. In early 2005, we find a shift from anti-correlation to correlation of magma-chamber inflation. The shift is preceded by a seismic swarm in the mantle beneath Mauna Loa and accompanied by a large silent slip event beneath the south flank of Kilauea. This suggests that these volcanoes are coupled during mantle-driven surges and that the 2005 silent slip event was triggered by accelerated magma supply at Kilauea.

[1] We estimated the P-wave velocity structure of the crust of the subducting Pacific plate beneath Northeast Japan using arrival-time data of P-to-S-converted waves. The results show that the P-wave velocity of the subducting crust varies along the arc and increases abruptly at a depth of ~100 km, from 6.5–7.0 km/s in the forearc to 7.5–8.5 km/s in the backarc. The P-wave velocity in the forearc is ~10% lower than theoretically expected values for the metamorphosed MORB material. Seismicity in the subducting crust is most active at depths of 70–80 km where P-wave velocities are lowest. The marked reduction of P-wave velocity suggests the co-existence of aqueous fluids with hydrous minerals. Abundant fluids elevate pore-fluid pressures and reduce effective normal stress, promoting intensive seismic activity in the low-velocity crust. Our observations provide seismic evidence that earthquakes in the subducting crust are facilitated by fluid-related embrittlement.

[1] Controversy remains over a discrepancy between modelled and observed tropical upper tropospheric temperature trends. This discrepancy is reassessed using simulations from the Coupled Climate Model Inter-comparison Project phase 5 (CMIP 5) togetherwith radiosonde and surface observations that provide multiple realizations of possible ‘observed’ temperatures given various methods of homogenizing the data. Over the 1979-2008 period tropical temperature trends are not consistent with observations throughout the depth of the troposphere, and this primarily stems from a poor simulation of the surface temperature trends. This discrepancy is substantially reduced when; 1) atmosphere-only simulations are examined or 2) the trends are considered as an amplification of the surface temperature trend with height. Using these approaches, it is shown that within observational uncertainty the 5-95 percentile range of temperature trends from both coupled-ocean and atmosphere-only models are consistentwith observations at all but the upper most tropospheric level (150 hPa), and models with ultra-high horizontal resolution (≤ 0.5° × 0.5°) perform particularly well. Other than model resolution, it is hypothesised that this remaining discrepancy could be due to a poor representation of stratospheric ozone, or remaining observational uncertainty.

[1] We present the very first simultaneous detection from space of a terrestrial gamma-ray flash (TGF) and the optical signal from lightning. By fortuitous coincidence two independent satellites passed less than 300 km from the thunderstormsystem that produced a TGF that lasted 70 µs. Together with two independent measurements of radio emissions we have an unprecedented coverage of the event. We find that the TGF was produced deep in the thundercloud at the initial stage of an intracloud (IC) lightning before the leader reached the cloud top and extended horizontally. A strong radio pulse was produced by the TGF itself. This is the first time the sequence of radio pulses, TGF and optical emissions in an IC lightning flash has been identified.

[1] While the seismic effects of wave-induced fluid flow due to mesoscopic heterogeneities have been studied for several decades, the role played by these types of heterogeneities on seismoelectric phenomena is largely unexplored. To address this issue, we have developed a novel methodological framework which allows for the coupling of wave-induced fluid flow, as inferred through numerical oscillatory compressibility tests, with the pertinent seismoelectric conversion mechanisms. Simulating the corresponding response of a water-saturated sandstone sample containing mesoscopic fractures, we demonstrate for the first time that these kinds of heterogeneities can produce measurable seismoelectric signals under typical laboratory conditions. Given that this phenomenon is sensitive to key hydraulic and mechanical properties, we expect that the results of this pilot study will stimulate further exploration on this topic in several domains of the Earth, environmental, and engineering sciences.

[1] When carbon dioxide (CO₂) dissolves into water, the density of water increases. This seemingly insubstantial phenomenon has profound implications for geologic carbon sequestration. Here we show, by means of laboratory experiments with analogue fluids, that the up-slope migration of a buoyant current of CO₂ is arrested by the convective dissolution that ensues from a fingering instability at the moving CO₂–groundwater interface. We consider the effectiveness of convective dissolution as a large-scale trapping mechanism in sloping aquifers, and we show that a small amount of slope is beneficial compared to the horizontal case. We study the development and coarsening of the fingering instability along the migrating current, and predict the maximum migration distance of the current with a simple sharp-interface model. We show that convective dissolution exerts a powerful control on CO₂ plume dynamics and, as a result, on the potential of geologic carbon sequestration.

[1] Hurricane Sandy drove storm surges throughout the eastern seaboard of the United States, from Miami to Maine, at the end of October 2012. The surge was particularly high (>3 m) in coastal New York. In the southeastern United States, the surge was <1 m but had striking semidiurnal perturbations that reached a range of ~0.5 m in northern Florida and southern Georgia. These oscillations are typically not considered in surge forecasts and their origin needs to be understood for future forecasts. Analytical and numerical approaches indicated that semidiurnal perturbations arose from an interaction between astronomical tide and wind forcing. This combination of forcing caused phase shifts between incident and reflected tidal waves that customarily produce quasi-standing tidal conditions in the area. Atmospheric forcing of sufficient strength, which threshold remains to be established, disrupted such quasi-standing tidal behavior through Coriolis accelerations and triggered the semidiurnal perturbations.

[1] Lakes have been identified as an important source of atmospheric methane. Here, the spatio-temporal distribution of dissolved methane was measured in a medium-sized freshwater lake. The data reveal that littoral zones (near-shore, shallow) are the predominant source of methane. Offshore-directed gradients of dissolved methane suggest the transport of methane from the near-shore zone to the pelagic epilimnion. The distribution patterns of epilimnetic methane were highly heterogeneous independent of the mean lake-wide methane concentration. Consequently, the diffusive flux of methane to the atmosphere strongly varies with location in the lake. A comparison of the diffusive methane flux from different offshore sampling stations indicates that single-point measurements are not necessarily sufficient to estimate lake-wide emissions to the atmosphere accurately. Thus, spatially resolved measurements of methane emissions are needed to improve the reliability of estimates of the methane that lakes contribute to the global methane budget.

[1] New particle formation consists of homogeneous nucleation of thermodynamically stable clusters followed by growth of these clusters to a detectable size. For new particle formation to take place, these clusters need to grow sufficiently fast to escape coagulation with pre-existing particles. Previous studies indicated that condensation of low-volatility organic vapor may play an important role in the initial growth of the clusters. However, due to the relatively high vapor pressure and partial molar volume of even highly oxidized organic compounds, the strong Kelvin effect may prevent typical ambient organics from condensing on these small clusters. Here we show that the adsorption of organic molecules onto the surface of clusters, not considered previously, may significantly reduce the saturation ratio required for the condensation of organics to occur, and therefore may provide a physico-chemical explanation for the enhanced initial growth by condensation of organics despite the strong Kelvin effect.

[1] The Naval Research Laboratory three-dimensional, first-principles simulation code SAMI3 (Sami3 is Also a Model of the Ionosphere) is used to model plasmasphere refilling. A time-dependent Volland-Stern-Maynard-Chen potential is used to model an idealized magnetic storm that erodes the plasmasphere to L < 3. The potential is then relaxed to the pre-storm state and refilling is simulated for a range of L shells 3 ≤ L≤ 5 over a period of 7 days. Refilling rates compare well to observed refilling rates. The model plasmasphere during this quiet period displays a day-to-day repetition in its morphology that has not been previously observed.

[1] The mass balance in the Inner Tibet Plateau (ITP) derived from satellite gravimetry (GRACE) showed a positive rate that was attributed to the glacier mass gain, whereas glaciers in the region, from other field-based studies, showed an overall mass loss. In this study, we examine lake's water level and mass changes in the Tibetan Plateau (TP) and suggest that the increased mass measured by GRACE was predominately due to the increased water mass in lakes. For the 200 lakes in the TP with 4 to 7 years of ICESat data available, the mean lake level and total mass change rates were +0.14 m/year and +4.95 Gt/year, respectively. Compared those in the TP, 118 lakes in the ITP showed higher change rates (+0.20 m/year and +4.28 Gt/year), accounting for 59% area and 86% mass increase of the 200 lakes. The lake's mass increase rate in the ITP explains the 61% increased mass (~7 Gt/year) derived from GRACE [Jacob et al., 2012], while it only accounts for 53% of the total lake area in the ITP.

[1] In this study we assess the role of altitude in determining the relative performance of temperature and precipitation as predictors of snowpack variability in Switzerland. The results indicate a linear relationship between altitude and the correlation of temperature (precipitation) with snowpack depth and duration. We identify a threshold altitude of approximately 1400 m a.s.l. (± 200 m, depending on the snow index considered), below which temperature is the main explanatory variable and above which precipitation is a better predictor of snowpack variability. The results also highlight that as climate warms the altitude at which temperature is the main constraint on snow accumulation increases. This has important implications for the future viability of snow-dependent economic sectors in Switzerland, where projections indicate a continuous warming during the course of the 21st century.

[1] Coastal upwelling zones may be at enhanced risk from ocean acidification as upwelling brings low aragonite saturation state (Ω_Ar) waters to the surface that are further suppressed by anthropogenic CO₂. Ω_Ar was calculated with pH, pCO₂, and salinity-derived alkalinity time-series data from autonomous pH and pCO₂ instruments moored on the Oregon shelf and shelf break during different seasons from 2007–2011. Surface Ω_Ar values ranged between 0.66 ± 0.04 and 3.9 ± 0.04 compared to an estimated pre-industrial range of 1.0 ± 0.1 to 4.7 ± 0.1. Upwelling of high-CO₂ water and subsequent removal of CO₂ by phytoplankton imparts a dynamic range to Ω_Ar from ~1.0 to ~4.0 between spring and autumn. Freshwater input also suppresses saturation states during the spring. Winter Ω_Ar is less variable than during other seasons and is controlled primarily by mixing of the water column.

[1] Acidified waters are impacting commercial oyster production in the U.S. Pacific Northwest and favorable carbonate chemistry conditions are predicted to become less frequent. Within 48 hours of fertilization, unshelled Pacific oyster (Crassostreagigas) larvae precipitate roughly 90% of their body weight as calcium carbonate. We measured stable carbon isotopes in larval shell and tissue and in algal food and seawater dissolved inorganic carbon in a longitudinal study of larval development and growth. Using these data and measured biochemical composition of larvae we show that sensitivity of initial shell formation to ocean acidification results from diminished ability to isolate calcifying fluid from surrounding seawater, a limited energy budget dependent, and a strong kinetic demand for calcium carbonate precipitation. Our results highlight an important link between organism physiology and mineral kinetics in larval bivalves and suggest the consideration of mineral kinetics may improve understanding winners and losers in a high CO₂ world.

[1] The North Atlantic eddy-driven jet is a major component of the large-scale flow in the northern hemisphere. Here we present evidence from reanalysis and ensemble forecast data for systematic flow-dependent predictability of the jet during northern hemisphere winter (DJF). It is found that when the jet is weakened or split it is both less persistent and less predictable. The lack of predictability manifests itself as the onset of an anomalously large instantaneous rate of spread of ensemble forecast members as the jet becomes weakened. This suggests that as the jet weakens or splits it enters into a state more sensitive to small differences between ensemble forecast members, rather like the sensitive region between the wings of the Lorenz attractor.

[1] The disparities in satellite based observations of global gravity wave activity are discussed in terms of methods used to extract the gravity wave perturbations from background and the sensitivity of the given satellite to the gravity wave spectrum. The temperature measurements from TIMED/SABER are used to obtain the global gravity wave maps in terms of their potential energies by employing two widely used methods to extract the gravity wave perturbations viz. (1) removal of 0–6 zonal wavenumber large-scale waves and (2) high pass filter with cut-off vertical wavelength at 10 km. The present study for the first time employed these two different methods on the same satellite observations to investigate the sensitivity of global gravity wave patterns and their magnitudes to the methods used to extract them. The results showed significant differences in the gravity wave potential energy magnitudes estimated by employing these two methods. Further, employing the first method on COSMIC measured temperature profiles, the global gravity wave pattern is estimated and the same is compared with that obtained using SABER observations. This comparison substantiated the assertion that by using the same method to extract the gravity wave perturbations from different satellite observations yields the similar global gravity wave pattern. The present study thus provided very useful insights into the observed discrepancies among current global gravity wave patterns and is envisaged that this is a step forward in unifying the existing methods to extract gravity wave parameters using space based observations.

[1] Amazon forests exert a major influence on the global carbon cycle but quantifying the impact is complicated by diverse landscapes and sparse data. Here we examine seasonal carbon balance in southern Amazonia using new measurements of column-averaged dry air mole fraction of CO₂ (XCO₂) and solar induced chlorophyll fluorescence (SIF) from GOSAT from July 2009 – December 2010.SIF, which reflects gross primary production (GPP), is used to disentangle the photosynthetic component of land-atmosphere carbon exchange. We find that tropical transitional forests in southern Amazonia exhibit a pattern oflowXCO₂during the wet season and high XCO₂in the dry season that is robust to retrieval methodology and with seasonal amplitude double that of cerrado ecosystems to the east (4 ppm vs 2 ppm), including enhanced dilution of 2.5 ppm in the wet season. Concomitant measurements of SIF, which are inversely correlated with XCO₂ in southern Amazonia (r = -0.53, p < 0.001), indicate the enhanced variability is driven by seasonal changes in GPP due to coupling of strong vertical mixing with seasonal changes in underlying carbon exchange. This finding is supported by forward simulations of GEOS-Chem which show that local carbon uptake in the wet season and loss in the dry season due to emissions by ecosystem respiration and biomass burning produces best agreement with observed XCO₂. We conclude that GOSAT provides critical measurements of carbon exchange in southern Amazonia but more samples are needed to examine moist Amazon forests farther north.

[1] We developed a new method to estimate terrestrial evapotranspiration (ET) from satellite data without using meteorological inputs. By analyzing observations from 20 eddy covariance tower sites across continental North America, we found a strong relationship between monthly gross primary production (GPP) and ET (R² = 0.72 ~ 0.97), implying the potential of using the remotely sensed GPP to invert ET. We therefore adopted the Temperature-Greenness model which calculates 16-day GPP using MODIS EVI and LST products to estimate GPP, and then to calculate ET by dividing GPP with ecosystem water use efficiency (the ratio of GPP to ET). The proposed method estimated 16-day ET very well by comparison with tower-based measurements (R² = 0.84, p < 0.001, n = 1290) and provided better ET estimates than the MODIS ET product. This suggests that routine estimation of ET from satellite remote sensing without using fine-resolution meteorological fields is possible and can be very useful for studying water and carbon cycles.

[1] We used 6 hours of continuous vertical records from 2320 sensors of the Valhall Life of Fields Seismic network to compute 2 690 040 cross-correlation functions between the full set of sensor pair combinations. We applied the ’Helmholtz tomography’ approach combined with the ambient noise correlation method to track the wave front across the network with every station considered as a virtual source. The gradient of the interpolated phase travel time gives us an estimate of the local phase speed and of the direction of wave propagation. By combining the individual measurements for every station, we estimated the distribution of Scholte's wave phase speeds with respect to azimuth. The observed cosine pattern indicates the presence of azimuthal anisotropy. The elliptic shape of the fast anisotropy direction is consistent with results of previous shear wave splitting studies and reflects the strong seafloor subsidence due to the hydrocarbon reservoir depletion at depth and is in good agreement with geomechanical modeling.

[1] The margins surrounding the Tibetan Plateau show some diversity in topographic gradient. The most striking example is the eastern Tibetan margin bordered by the Longmen Shan range, which is characterized by a remarkably steep topography transition between eastern Tibet and the Sichuan Basin. There is significant uncertainty over whether this margin was formed by crustal shortening or lower crustal flow. To investigate the formation mechanism of steep convergent intracontinental margins, we conducted petrological-thermomechanical numerical simulations based on the lithospheric structure and thermal state of the eastern Tibetan margin. Our numerical experiments demonstrate that a very steep topographic gradient, such as the eastern Tibetan margin, is an inherent characteristic of convergence between a hot and weak lithosphere with thick crust and a cold and strong lithosphere with thin crust. Although lower crustal flow has potentially contributed to the crustal thickness difference between the two convergent blocks, it is not a prerequisite for the growth of steep convergent intracontinental margin. Rather, the topography at the margin can be explained by a near isostatic response to crustal thickening resulting from shortening.

[1] We investigated the relationship between the systematic annual and semiannual variations in the ionosphere and thermosphere using a combination of data analysis and model simulation. A climatology of daytime peak density and height of the ionospheric F₂-region was obtained from GPS radio occultation measurements by the Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) during 2007–2010. These measurements were compared to simulations by the NCAR Thermosphere-Ionosphere-Electrodynamics General Circulation Model (TIE-GCM). Model reproduction of the ionospheric annual and semiannual variations was significantly improved by imposing seasonal variation of eddy diffusion at the lower boundary, which also improves agreement with thermospheric density measurements. Since changes in turbulent mixing affect both the thermosphere and ionosphere by altering the proportion of atomic and molecular gases, these results support the proposition that composition change drives the annual/semiannual variation in both the neutral and ionized components of the coupled system.

[1] The relationships between fractional entrainment rate and key microphysical quantities (e.g., liquid water content, droplet number concentration, volume-mean radius, standard deviation of cloud droplet size distributions) in shallow cumuli are empirically examined using in situ aircraft observations from the RACORO field campaign over the ARM SGP site. The result shows that the microphysical quantities examined generally exhibit strong relationships with entrainment rate, and that the relationships collectively suggest the dominance of homogeneous entrainment mixing, which is unfavorable to the formation of large droplets and the initiation of warm rain in these clouds. The dominance of the homogeneous mixing mechanism is further substantiated by the dependency on entrainment rate of relationships among various microphysical variables and of cloud droplet size distributions. The dominance of homogeneous mixing mechanism is also quantitatively confirmed by examining the degree of homogeneous mixing in these clouds. The dominance of homogeneous mixing may be an important reason why none of these cumulus clouds were drizzling.

[1] Foreshocks are one of the few well-documented precursors to large earthquakes; therefore, understanding their nature is very important for earth quake prediction and hazard mitigation. However, the triggering role of foreshocks is not yet clear. It is possible that foreshocks are a self-triggering cascade of events that simply happen to trigger an unusually large aftershock; alternatively, foreshocks might originate from an external aseismic process that ultimately triggers the mainshock. In the former case, the foreshocks will have limited utility for forecasting. The latter case has been observed for several individual large earthquakes, however, it remains unclear how common it is, and how to distinguish foreshock sequences from other seismicity clusters that do not lead to large earthquakes. Here, we analyze foreshocks of three M > 7 mainshocks in southern California. These foreshock sequencesappear similar to earthquake swarms, in that they do not start with their largest events and they exhibit spatial migration of seismicity. Analysis of source spectra shows that all three foreshock sequences feature lower average stress drops and depletion of high-frequency energy compared with the aftershocks of their corresponding mainshocks. Using a longer-term stress drop catalog, we find that the average stress drop of the Landers and Hector Mine foreshock sequences are comparable to nearby swarms. Our observations suggest that these foreshock sequences are manifestations of aseismic transients occurring close to the mainshock hypocenters, possibly related to localized fault zone complexity, which have promoted the occurrence of both the foreshocks and the eventual mainshocks.

[1] The relationship between cloud-top entrainment and cloud hole size at the top of stratocumulus clouds is explored with large-eddy simulations and a Lagrangian parcel tracking model. The cloud-hole size distribution follows a negative power law, in excellent agreement with satellite observation at 15 m resolution. As a result of the steep decrease in the number of holes with increasing size, the number of entrained Lagrangian parcels also decreases with increasing hole size (negative power law), even though the number of entrainment events per hole increases with increasing hole size (positive power law). Thus entrainment preferentially occurs in small holes. Further analysis shows that the domain averaged entrainment velocity is a reasonable approximation to the domain averaged cloud-hole vertical velocity, and dominated by contributions from the small holes.

[1] The dominant neutral constituent in Earth's upper exosphere, atomic hydrogen (H), resonantly scatters solar Lyman-alpha (121.567 nm) radiation, observed as the geocorona. We report here observations of an exospheric response to geomagnetic storms obtained using measurements of the geocorona by Lyman-alpha Detectors (LADs) on the Two Wide-angle Imaging Neutral-atom Spectrometers (TWINS) mission. We introduce a new parameter, N_H, the number of H atoms in the spherical shell from a geocentric distance of 3 to 8 Earth radii, to quantitatively characterize in a simplified way global exospheric conditions. Five geomagnetic storms observed during three months in the second half of 2011 are accompanied by abrupt temporary increases, spikes, of N_H from 6% to 17%, lasting not longer than a day. These increases seem to show some correlation with the minimum Dst index reached during the peak of each storm.

[1] Natural aerosol plays a significant role in the Earth system due to its ability to alter the radiative balance of the Earth. Here we use a global aerosol microphysics model together with a radiative transfer model to estimate radiative effects for five natural aerosol sources in the present-day atmosphere: dimethyl sulfide (DMS), sea-salt, volcanoes, monoterpenes and wildfires. We calculate large annual global mean aerosol direct and cloud albedo effects especially for DMS-derived sulfate (-0.23 Wm^-2 and -0.76 Wm^-2, respectively), volcanic sulfate (-0.21 Wm^-2 and -0.61 Wm^-2) and sea-salt (-0.44 Wm^-2 and -0.04 Wm^-2). The cloud albedo effect responds non-linearly to changes in emission source strengths. The natural sources have both markedly different radiative efficiencies and indirect/direct radiative effect ratios. Aerosol sources that contribute a large number of small particles (DMS-derived and volcanic sulfate) are highly effective at influencing cloud albedo per unit of aerosol mass burden.

[1] We perform a series of 3D Direct Numerical Simulations (DNS) to assess the vertical heat transport through thermohaline staircases in the Arctic Ocean. The diagnostics of DNS, performed for the first time in the realistic parameter range, result in vertical fluxes exceeding those of extant “four-thirds flux laws” by as much as a factor of 2, and suggest that the 4/3 exponent may require downward revision. Through a series of equivalent 2D DNS, we show that they are consistent with their more resource-intensive 3D counterparts for sufficiently large density ratio (R_ρ) but underestimate heat transport for low  R_ρ. Finally, we examine the role of boundary conditions in controlling the vertical heat transport. Rigid boundaries – a necessary ingredient in laboratory-derived flux-laws – are shown to reduce the estimates of heat fluxes relative to the corresponding periodic boundary conditions.

[1] At the end of the global thermohaline circulation, the subarctic Pacific is the richest nutrient repository in the world oceans. Trends towards lower oxygen and higher nutrients in waters below the surface layer (the pycnocline) have been observed in recent decades. We assess these trends using data from four programs and suggest the enrichment of pycnocline nitrate (200 Gmol y^-1) is essential in keeping supply to the surface ocean constant, despite increasing upper ocean stratification. A nitrate budget helps identify possible vertical processes that could account for nutrient redistribution. We hypothesize that warming and oxygen loss in the deeper pycnocline, arising from ice loss in the Okhotsk Sea, have initiated a largely vertical redistribution of nutrients due to compression of vertical migrator habitat and/or changes in dissolution of sinking particulates. Coupled climate-ecosystem models will need to incorporate these processes to more fully understand projected changes in the subarctic Pacific.

[1] Studying variations of the stress field in reservoirs caused by massive fluid injection is important towards an improved understanding of geomechanical processes involved. We report on spatio-temporal variations of the local stress tensor orientation at The Geysers geothermal field, California. We apply two stress inversion methods with detailed uncertainty assessments using a selection of events recorded between 2007 and 2012. Our results clearly indicate variations in the orientation of the principal stress axes for the reservoir as a whole showing a normal faulting regime at the reservoir depth between 2 and 3.7 km bounded by a strike-slip regime above and below. Analyzing the temporal evolution of the stress tensor orientation for a prominent seismicity cluster we observe a clear correlation of changes in orientation for σ_1-3 with the highest injection rates. These results suggest that temporal changes in the stress tensor orientation could contribute to characterize reservoirs during stimulation.

[1] This study investigates relationships between variability in the Pacific and extreme rainfall in eastern Australia. Using an index of extreme precipitation derived from a daily gridded precipitation dataset from 1900 to 2011, we find a non-linear relationship between ENSO and extreme rainfall exists. That is the strength of a La Niña episode has a much greater influence on the intensity and duration of extreme rainfall than the magnitude of an El Niño episode. This relationship is found in both interpolated observations and reanalysis data, and may be explained, in part, by shifts in the divergence of moisture flux. There is significant decadal variability in the relationship, such that the asymmetry is enhanced during Interdecadal Pacific Oscillation (IPO) negative events and is non-existent during IPO positive phases. This information has the potential to be of great use in the seasonal prediction of intense rainfall events that lead to flooding.

[1] Loess deposits in Asia have been used as indicators of palaeoclimate, as they are usually found bordering deserts. This paper reports extensive and thick deposits of loess in tropical southwest China, between latitudes 18 and 23º30’ north, which is 1300 km south of known, and extensively researched loess deposits in north China. Present climate of the reported loess areas is hot and humid, with mean annual rainfall of 1000-2000 mm, and vegetation of sub-tropical evergreen broadleaf forest. This compares with less than 400 mm rainfall and vegetation of semi-desert steppe, in areas of current loess accumulation on desert margins in north China. The source area of the loess, which is dated by optical luminescence to the late Pleistocene, from 90-222 ka, is thought to be the exposed East Asian Shelf which was up to 140 m below present sea level during Quaternary arid phases. Recent research on the nature of the shelf environment, as well as the relatively large particle size of the loess, suggests a local origin. The reported loess is not interbedded with palaeosols, and small amounts of soil cover the loess, compared with well developed soils in loess in semi-arid regions in north China. This is explained by elimination of the supply source by sea level rise following each arid phase, as continued dust supply appears necessary for soil to form. This preliminary report of loess in southwest China conflicts with palynological evidence, and suggests that recent reconstructions of Pleistocene aridity in east Asia may be conservative.

[1] Analysis of observational datasets reveals pronounced interannual variations of sea surface salinity (SSS) in the tropical North Pacific (TNP; 7°–15° N) during 2000–2012. SSS anomalies with maximum magnitudes > 0.2 occur in the central Pacific and translate westward at a speed of 15–20 cm s^-1. The signals are weakened during their westward movement but reinforced in the Philippine Sea. Budget analysis for the mixed layer salinity suggests that in the central Pacific, ENSO-related atmospheric freshwater forcing and ocean advection changes are both important in generating and maintaining these large SSS anomalies. In the advection term, the most contributing component is the meridional Ekman advection induced by trade winds. These SSS anomalies are subsequently carried westward by the North equatorial Current (NEC), which is the primary cause of SSS variations in the Philippine Sea. Freshwater forcing is also at work in the Philippine Sea, but its role is generally secondary.

[1] To improve our understanding of the complex coupling between circulating fluids and the development of crack damage we have performed flow-through tests on samples of Etna Basalt and Westerly granite that were cyclically loaded by deviatoric stresses. The basalt is naturally micro-fractured, while the relatively crack-free Westerly granite was thermally pre- treated to 500 °C and 800 °C to generate micro-crack damage. Samples were repeatedly loaded and then unloaded under deviatoric stress paths and ultimately to failure. Permeability and water volume content were measured throughout the loading history together with the differential stress. Permeability decreases at low differential stresses and increases at intermediate differential stresses up to a steady value at failure. We use water volume content as a proxy for fluid storage and show that both permeability and storage evolve with damage and evolution of crack density. We use crack models to represent the evolution of permeability as a function of loading state and are able to independently link the evolution of permeability to the observed evolution of deformability, used as an independent measure of crack density.

[1] Several Mediterranean vortices with characteristics similar to tropical cyclones are analyzed by means of numerical simulations, satellite products and lightning data. Numerical analysis suggests that the broad tropical-like cyclone category includes in reality a set of different cyclones, ranging from very small and weak vortices to larger and stronger cyclones. One case displays a much longer persistence of tropical features than the other events. The analysis of the tracks identifies two preferred areas of occurrence, the Ionian sea and the Balearic Islands. The satellite analysis of cloud top height and retrieved rainfall indicates that the stage characterized by the most intense convective activity and rainfall anticipates the mature phase, when the cyclone is more intense and characterised by tropical features, during which convection is shallower and rainfall weaker. This result is confirmed by a preliminary analysis of the lightning activity.

[1] The western North Pacific (WNP) Subtropical High (WNPSH) is a controlling system for East Asian Summer monsoon and tropical storm activities, whereas what maintains the anomalous summertime WNPSH has been a long-standing riddle. Here we demonstrate that the local convection-wind-evaporation-SST (CWES) feedback relying on both mean flows and mean precipitation is key in maintaining the WNPSH, while the remote forcing from the development of El Niño/Southern Oscillation is secondary. Strikingly, the majority of strong WNPSH cases exhibit anomalous intensification in late summer (August), which is dominantly determined by the seasonal march of the mean state. That is, enhanced mean precipitation associated with strong WNP monsoon trough in late summer make atmospheric response much more sensitive to local SST forcing than early summer.

[1] Based on periodicities in the kilometric radio emissions, the Saturn Longitude System 4 (SLS4), was used to organize the far ultraviolet (120–150 nm) aurora observed by the Ultraviolet Imaging Spectrograph (UVIS) on the Cassini spacecraft. Individual UVIS pixels were projected onto the ionosphere of Saturn, transformed into the SLS4 north and SLS4 south longitude systems, accumulated over all over auroral observations from 2007 to early 2009, and binned into 1°x 1° bins of co-latitude. The intensity of the northern aurora showed little variation in its SLS4 north system, but the intensity of the southern aurora exhibited an enhancement of over ~10 kR between ~140–280° SLS4 south longitude. This enhancement may represent the auroral signature of a southern ionospheric vortex proposed in MHD models of Saturn's magnetosphere to explain its periodicities. The loci of the northern intensity peaks and the 3 kR boundaries varied little over 360° of longitude, while the equatorward boundary of the southern aurora varied by ~5° in SLS4 south longitude, reaching its most equatorward location of ~23° colatitude between 100° and 180° longitude. The polygonal centroids of the aurora in both north and south were consistent with offsets of no more than ~1° in both hemispheres.

[1] This study evaluates four years (2009–12) of World Wide Lightning Location Network (WWLLN)data relative to the Tropical Rainfall Measurement Mission (TRMM) Lightning Imaging Sensor (LIS). In the Western Hemisphere between 38° N and 38° S,WWLLN detection efficiency (of LIS flashes)steadily improves from 6% during 2009 to 9.2% during 2012. WWLLN is ~ 3 times more likely to detecta LIS flashover the ocean(17.3%) than over land (6.4%), and detection efficiencies greater than 20% only occur over the oceans. An average of1.5 WWLLN strokes occur during each matched LIS flash, but 71.5% of matched flashes are single stroke. Matched LIS flashes have more events/groups, longer durations, and larger areas than non-matched flashes. The close spatial (11 km) and temporal (+62 ms) proximity between matched WWLLN and LIS flashes is important for Geostationary Lighting Mapper (GLM) risk-reduction studies that use existing networks to developproxy datasets.

[1] Confidence in estimates of anthropogenic climate change is limited by known issues with air temperature observations from land stations. Station siting, instrument changes, changing observing practices, urban effects, land cover, land use variations, and statistical processing have all been hypothesized as affecting the trends presented by the Intergovernmental Panel on Climate Change and others. Any artifacts in the observed decadal and centennial variations associated with these issues could have important consequences for scientific understanding and climate policy. We use a completely different approach to investigate global land warming over the 20^th century. We have ignored all air temperature observations and instead inferred them from observations of barometric pressure, sea surface temperature, and sea-ice concentration using a physically-based data assimilation system called the 20^th Century Reanalysis. This independent dataset reproduces both annual variations and centennial trends in the temperature datasets, demonstrating the robustness of previous conclusions regarding global warming.

[1] Field studies of watershed carbon fluxes and budgets are critical for understanding the carbon cycle, but the role of deep regional groundwater is poorly known and field examples are lacking. Here we show that discharge of regional groundwater into a lowland Costa Rican rainforest has a major influence on ecosystem carbon fluxes. This influence is observable through chemical, isotopic, and flux signals in groundwater, surface water, and air. Not addressing the influence of regional groundwater in the field measurement program and data analysis would give a misleading impression of the overall carbon source or sink status of the rainforest. In quantifying a carbon budget with the traditional " small watershed" mass-balance approach, it would be critical at this site and likely many others to consider watershed inputs or losses associated with exchange between the ecosystem and the deeper hydrogeological system on which it sits.

[1] Old Faithful Geyser in Yellowstone National Park (USA) has attracted numerous scientific investigations for over two centuries in order to better understand its geological structure, the physics of its eruptions, and the controls of its intermittency. Using data acquired with a seismic array in 1992, we track the sources of hydrothermal tremor produced by boiling and cavitation inside the geyser. The location of seismic sources identifies a previously unknown lateral cavity at 15 m below the surface, on the SW side of the vent, and connected to the conduit. This reservoir is activated at the beginning of each geyser eruption cycle and plays a major role in the oscillatory behavior of the water level in the conduit before each eruption.

[1] In this study, we find from analyses of projections of 14 CMIP5 models a robust, canonical global response in rainfall characteristics to a warming climate. Under a scenario of 1% increase per year of CO₂ emission, the model ensemble projects globally more heavy precipitation (+7 ± 2.4%K^-1), less moderate precipitation (-2.5 ± 0.6%K^-1), more light precipitation (+1.8 ± 1.3%K^-1), and increased length of dry (no-rain) periods (+4.7 ± 2.1%K^-1). Regionally, a majority of the models project a consistent response with more heavy precipitation over climatologically wet regions of the deep tropics especially the equatorial Pacific Ocean and the Asian monsoon regions, and more dry periods over the land areas of the subtropics and the tropical marginal convective zones. Our results suggest that increased CO₂ emissions induce a global adjustment in circulation and moisture availability manifested in basic changes in global precipitation characteristics, including increasing risks of severe floods and droughts in preferred geographic locations worldwide.

[1] Infragravity waves (IGWs) play an important role in coupling wave processes in the ocean, ice shelves, atmosphere, and the solid Earth. Due to the paucity of experimental data, little quantitative information is available about power spectra of IGWs away from the shore. Here, we use continuous, yearlong records of pressure at 28 locations on the seafloor off New Zealand's South Island to investigate spectral and spatial distribution of IGW energy. Dimensional analysis of diffuse IGW fields reveals universal properties of the power spectra observed at different water depths and leads to a simple, predictive model of the IGW spectra. While sources of IGWs off New Zealand are found to have a flat power spectrum, the IGW energy density has a pronounced dependence on frequency and local water depth as a result of the interaction of the waves with varying bathymetry.

[1] A two-dimensional numerical simulation of lithospheric shortening shows the formation of a stable crustal-scale shear zone due to viscous heating. The shear zone thickness is controlled by thermo-mechanical coupling that is resolved numerically inside the shear zone. Away from the shear zone lithospheric deformation is dominated by pure shear, and tectonic overpressure (i.e. pressure larger than the lithostatic pressure) is proportional to the deviatoric stress. Inside the shear zone deformation is dominated by simple shear, and the deviatoric stress decreases due to thermal weakening of the viscosity. To maintain a constant horizontal total stress across the weak shear zone (i.e. horizontal force balance) the pressure in the shear zone increases to compensate the decrease of the deviatoric stress. Tectonic overpressure in the weak shear zone can be significantly larger than the deviatoric stress at the same location. Implications for the geodynamic history of tectonic nappes including HP-UHP rocks are discussed.

[1] The Gutenberg-Richter (GR) frequency-magnitude relation is a fundamental empirical law of seismology, but its form remains uncertain for rare extreme events. Here we show that the temporal evolution of model likelihoods and parameters for the frequency-magnitude distribution of the global Harvard Centroid Moment Tensor catalogue is inconsistent with an unbounded GR relation, despite it being the preferred model at the current time. During the recent spate of twelve great earthquakes in the last 8 years, record-breaking events result in profound steps in favour of the unbounded GR relation. However, between such events the preferred model gradually converges to the tapered GR relation, and the form of the convergence cannot be explained by random sampling of an unbounded GR distribution. The convergence properties are consistent with a global catalogue composed of superposed randomly-sampled regional catalogues, each with different upper bounds -many of which have not yet sampled their largest event.

[1] The International Bathymetric Chart of the Southern Ocean (IBCSO) Version 1.0 is a new digital bathymetric model (DBM) portraying the seafloor of the circum-Antarctic waters south of 60° S. IBCSO is a regional mapping project of the General Bathymetric Chart of the Oceans (GEBCO). IBCSO Version 1.0 DBM has been compiled from all available bathymetric data collectively gathered by more than 30 institutions from 15 countries. These data include multibeam and single beam echo soundings, digitized depths from nautical charts, regional bathymetric gridded compilations, and predicted bathymetry. Specific gridding techniques were applied to compile the DBM from the bathymetric data of different origin, spatial distribution, resolution, and quality. The IBCSO Version 1.0 DBM has a resolution of 500 x 500 m, based on a polar stereographic projection, and is publicly available together with a digital chart for printing from the project website (www.ibcso.org) and at http://dx.doi.org/10.1594/PANGAEA.805736.

[1] A global contrast between oceanic and continental lightning very low frequency energy is observed using the World Wide Lightning Location Network (WWLLN). Strokes over the ocean are found to be stronger on average than those over land with a sharp boundary along a majority of coastlines. A linear regression method is developed to account for the spatial and temporal variation of WWLLN in order to perform a multi-year and global analysis of stroke energy distributions.

[2] The results are corroborated with data from the Lightning Imaging Sensor, the Optical Transient Detector, and the Earth Networks Total Lightning Network. These systematic comparisons lead to the conclusion that there exists a strong difference in the energetics between land and ocean thunderstorms that results in a higher fraction of more powerful strokes over the oceans.

[1] We assess initial-value predictability characteristics of Antarctic sea ice from climate simulations. The integrations are initialized on January 1^st with identical ice-ocean-terrestrial conditions and integrated forward for two years. We find that the initialized ice-ocean state provides predictive capability on the ice-edge location around Antarctica for the first several months of integration. During the ice advance season from April to September, significant predictability is retained in some locations with an eastward propagating signal. This is consistent with previous work suggesting the advection of sea ice anomalies with the mean ocean circulation. The ice-edge predictability is then generally lost during the ice retreat season after October. However, predictability reemerges during the next years ice advance starting around June in some locations. This reemergence is associated with ocean heat content anomalies that are retained at depth during the austral summer and resurface during the following autumn as the ocean mixed layers deepen.

[1] Eruption dynamics are sensitive to ash aggregation, and aggregates are commonly found in eruptive deposits. While ash dispersal and associated hazards are sensitive to aggregation, few experiments have been conducted on this phenomena using natural materials across the diverse range of conditions expected in volcanic flows. We have isolated two regimes, wet and dry, in which aggregation occurs due to two different forces, electrostatic and hydrodynamic. Using a closed chamber to create a controlled atmosphere, we found that relative humidity, residence time and kinetic energy are the three variables necessary to define wet and dry flow regimes. A series of process-based equations defining the behavior of ash particles have been developed. We propose an aggregation model that can be used for ash dispersal forecasts across a range of conditions in an eruptive plume.

[1] We present evidence that the springtime western boundary current (WBC) in the Bay of Bengal is a continuous northward-flowing current from about 12°N to 17°N, which then separates from the coast at around 18°N. We first revisit a hydrographic dataset collected in 1987 (Babu et al., 2003), from a potential vorticity perspective, and then analyze absolute dynamic height maps from satellite altimeters during the period 2000–2010. The altimetric maps suggest that the mean configuration of the WBC is that of an intense current with two anticyclonic eddies on the offshore side, which are part of the basin-wide anticyclonic circulation. The WBC consistently separates from the coast at around 18°N in all years between 2000 and 2010. The path of the eastward-flowing mean stream after separation appears to be consistent with isolines of f/H and with Ertel's potential vorticity, based on an analysis of the hydrographic data from 1987.

[1] This study uses the MRI high-resolution Atmospheric Climate Model to determine whether environmental parameters that control tropical cyclone (TC) genesis in the Western North Pacific (WNP) and North Atlantic (NA) may differ in the global warming state. A box difference index (BDI) was computed to quantitatively assess the role of environmental controlling parameters. The diagnosis of the model outputs shows that in the WNP, dynamic variables are of primary importance for separating developing and non-developing disturbances in the present-day climate, and such a relationship remains unchanged in a future warmer climate. This is in contrast to the NA, where BDI increases for all dynamic variables investigated while it shows little change for thermodynamic variables. This implies that, when compared with the present-day climate in which thermodynamic variables have a major control on TC genesis, dynamic and thermodynamic variables have equal control in the NA under the future warmer climate.

[1] Biomass burning aerosols from the tropical savanna of Northern Australia constitute a globally significant aerosol source, with impacts on regional climate and air quality. Knowledge of the seasonal cycle and spatial distribution of this aerosol is required for its realistic representation in models of global climate, and to help define the role of this region in the global carbon cycle. This paper presents a decadal climatology of these aerosols, based on sun photometer records from three stations in the Australian tropics, over the period 1998–2012. The monthly time series shows enhanced aerosol emissions following prodigious wet seasons, two of which occurred during the study period. The monthly climatology shows the expected peak during the late dry season (September-November), when most burning takes place, with clear evidence of the dominant modulating effect of fine-particle smoke emission apparent from the annual cycle of the Ångström exponent, a proxy for particle size. The aerosol levelsduring the early dry season are higher at the northern ’Top End’ stations than at the south-westerly Kimberley station. The time variation of aerosol optical depth is highly correlated between all three station pairs, with a correlation coefficient r² > 0.75 at monthly resolution between all pairs. This high correlation between widely-separated stations declines only gradually as the filtering interval is reduced, suggesting remarkably high coherence in the emission and transport of biomass burning aerosol across the entire region.

[1] Simulating the emission of mineral dust and sea-salt aerosol is non-linear with surface winds and requires accurate representation of surface winds. Consequently, the resolution of a simulation affects emission and is often corrected with non-physical scaling in coarse resolution global models. We examine the resolution dependence of emissions in the GEOS-Chem model and find that globally, annual emissions at 4° x 5° resolution are 59% of those simulated at 2° x 2.5° and only 33% of emissions at 0.25° x 0.3125°. The spatial and seasonal distribution of dust emissions vary substantially, indicating that applying a uniform scaling is inappropriate. We demonstrate the benefit of characterizing the sub-grid surface wind as a Weibull probability distribution, reconciling much of the difference in emissions between resolutions for dust. Such a representation is shown to have little impact on sea-salt emissions.

[1] Low frequency radio noise is the electromagnetic background radiation which is compared here to the luminosity of 39 sprites recorded with a low light video camera. It is found that the sprite luminosities coincide with ~10-30 ms long sudden enhancements of the electromagnetic background radiation ~6-8μVm^-1Hz^-1/2 (~6-9 dB) with a relative maximum near ~125 kHz as measured with a wideband (~1-400 kHz) digital radio receiver. The sprites cluster in 10 groups of 2-5 consecutive sprites which are paralleled by up to ~1 s long slowly varying enhancements of the electromagnetic background radiation ~4-5 μVm^-1Hz^-1/2 (~2-4 dB). The observed electric field strengths place an upper bound on the low frequency radiation from the electron multiplication associated with the exponential growth and branching sprite streamers predicted by [19]. This upper bound corresponds to a maximum of ~300-5000 sprite streamers at ~40 km height above thunderclouds. Some part of the observed electromagnetic background radiation might result from the superposition of low frequency radiation emanating from the quick succession of numerous horizontal lightning strokes and/or stepped leaders inside thunderclouds which would constitute a fundamentally novel quasi-static discharge process inside thunderclouds radiating slowly varying low frequency radio noise.

[1] Using 25 observations of damped oscillatory flow behavior in the near-Earth plasma sheet by the five THEMIS probes during the 2008-2009 magnetotail seasons, we derive the parameters of an oscillating thin filament, such as its oscillation period, damping factor, and entropy. To facilitate comparison with theory, we use measured pressures and magnetic fields with an empirical model to achieve a quantitative representation of the overall structure of the plasma sheet during each event. Because the observed oscillation period of the filament agrees with the oscillation period predicted by [30], the observed damped oscillatory flow behavior in the near-Earth plasma sheet is most likely caused by oscillatory braking of the filament.

[1] The variability of European summer climate is expected to increase in the next century due to increasing levels of atmospheric greenhouse gases, likely resulting in more frequent and more extreme droughts and heatwaves. However, climate models diverge on the magnitude of these processes, due to land-surface coupling processes which are difficult to simulate, and poorly constrained by observations. Here we use gridded observation-based sensible heat fluxes to constrain climate change predictions from an ensemble of 15 regional climate models. Land heat flux observations suggest that temperature projections may be underestimated by up to 1 K regionally in Central to Northern Europe, while slightly overestimated over the Mediterranean and Balkan regions. The use of observation-based heat flux data allows significant reductions in uncertainty as expressed by the model ensemble spread of temperature for the 2071–2100 period. Maximal reduction is obtained over France and the Balkan with values locally reaching 40%.

[1] Column-averaged dry air mole fractions of carbon dioxide (XCO₂) measured by the Greenhouse Gases Observing Satellite (GOSAT) reveal significant interannual variation (IAV) of CO₂ uptake during the Northern Hemisphere summer between 2009 and 2010. The XCO₂ drawdown in 2010 is shallower than in 2009 by 2.4 ppm and 3.0 ppm over North America and Eurasia, respectively. Reduced carbon uptake in the summer of 2010 is most likely due to the heat wave in Eurasia driving biospheric fluxes and fire emissions. A joint inversion of GOSAT and surface data estimates an integrated biospheric and fire emission anomaly in April–September of 0.89 ± 0.20 PgC over Eurasia. In contrast, inversions of surface measurements alone fail to replicate the observed XCO₂ IAV and underestimate emission IAV over Eurasia. This shows the value of GOSAT XCO₂ in constraining the response of land-atmosphere exchange of CO₂ to climate events.

[1] Given the paucity of observations, a great deal of uncertainty remains concerning temperature changes at very high altitudes over the last century. Englacial temperature measurements performed in boreholes provide a very good indicator of atmospheric temperatures for very high elevations although they are not directly related to air temperatures. Temperature profiles from seven deep boreholes drilled at three different sites between 4240 and 4300 m a.s.l. in the Mont Blanc area (French Alps) have been analyzed using a heat flow model and a Bayesian inverse modeling approach. Atmospheric temperature changes over the last century were estimated by simultaneous inversion of these temperature profiles. A mean warming rate of 0.14 ° C/decade between 1900 and 2004 was found. This is similar to the observed regional low altitude trend in the northwestern Alps, suggesting that air temperature trends are not altitude dependent.

[1] The cross-equatorial flow over the western Indian Ocean, known as the Findlater Jet, plays an important role in the monsoonal circulation of the region. During the boreal summer, there is southerly flow across the equator that is concentrated along the East African highlands. During the boreal winter, there is a reversal in wind direction across the equator. Madagascar, the world's fourth largest island, with heights in excess of 1 km represents a significant obstacle to the flow whose impact on this jet has not been fully characterized. Here we use diagnostic tools developed to investigate atmospheric flow distortion by Greenland's high topography to study this interaction. We show that there is a bifurcation of the Findlater Jet by Madagascar during the boreal summer as well as localized tip jets at the island's northern and southern ends. During the boreal winter, the northern tip jet reverses direction and weakens, while the southern tip jet maintains its direction and magnitude. We show that rotational effects are important for these interactions but not dominant and result in an enhancement of the northern tip jet; while allowing for existence of the southern tip jet. As will also be shown, this flow distortion has impacts on the meteorology and oceanography of the region including the forcing of oceanic eddies in the Mozambique Channel, a modulation of the southwards displacement of the ITCZ and a splitting of the boreal summer cross-equatorial mass transport associated with the Findlater Jet into two branches.

[1] We show how fully distributed space - time measurements with Fiber-Optic Distributed Temperature Sensing (FO-DTS) can be used to investigate groundwater flow and heat transport in fractured media. Heat injection experiments are combined with temperature measurements along fiber optic cables installed in boreholes. Thermal dilution tests are shown to enable detection of cross - flowing fractures and quantification of the cross flow rate. A cross borehole thermal tracer test is then analyzed to identify fracture zones that are in hydraulic connection between boreholes and to estimate spatially distributed temperature breakthrough in each fracture zone. This provides a significant improvement compared to classical tracer tests, for which concentration data are usually integrated over the whole abstraction borehole. However, despite providing some complementary results, we find that the main contributive fracture for heat transport is different to that for a solute tracer.

[1] Using the ERA40 reanalysis data, we study the different roles of synoptic and low-frequency eddies in sustaining the latitudinal shift of the low-level baroclinicity associated with SAM. The eddy effect is assessed through the direct eddy thermal forcing via eddy heat flux and the indirect forcing via eddy-driven Mean Meridional Circulation (MMC). We find that, in addition to the synoptic eddy-induced MMC suggested by [18], the direct eddy thermal forcing by low-frequency eddies is significant in driving the baroclinic anomalies. These two processes together prevail over the direct baroclinicity deduction by synoptic eddies. The different effects of synoptic and low-frequency eddies might be attributed to the distinct latitudinal distributions of their low-level eddy heat flux relative to the midlatitude jet. The different roles of the MMC induced by synoptic eddy momentum and heat flux are also emphasized, with the former leading the baroclinic anomalies and the latter acting to extend the baroclinic anomalies.

[1] Hurricane Sandy's track crossed the New Jersey coastline at an angle closer to perpendicular than any previous hurricane in the historic record, one of the factors contributing to record setting peak-water levels in parts of New Jersey and New York. In order to estimate the occurrence rate of Sandy-like tracks we use a stochastic model built on historical hurricane data from the entire North Atlantic to generate a large sample of synthetic hurricanes. From this synthetic set we calculate that under long-term average climate conditions a hurricane of Sandy's intensity or greater (category 1+) makes NJ landfall at an angle at least as close to perpendicular as Sandy's at an average annual rate of 0.0014 yr^-1 (95% confidence range 0.0007 to 0.0023); i.e., a return period of 714 yr (95% confidence range 435 to 1429).

[1] Subthermocline circulation in the tropical North Pacific Ocean (2°-30°N) is investigated using profiling float temperature–salinity data from the International Argo and the Origins of the Kuroshio and Mindanao Current (OKMC) projects. Three well-defined eastward jets are detected beneath the wind-driven, westward-flowing North Equatorial Current. Dubbed the North Equatorial Undercurrent (NEUC) jets, these subthermocline jets have a typical core velocity of 2–5 cm s^-1 and are spatially coherent from the western boundary to about 120°W across the North Pacific basin. Centered around 9°N, 13°N, and 18°N in the western basin, the NEUC jet cores tend to migrate northward by ~ 4° in the eastern basin. Vertically, the cores of the southern, central, and northern NEUC jets reside on the 26.9, 27.2, and 27.3 σ_θ surfaces, respectively, and they tend to shoal to lighter density surfaces, by about 0.2 σ_θ, as the jets progress eastward.

[1] HF cross-modulation is employed to probe the D-region ionosphere during HF heating experiments at the High-frequency Active Auroral Research Program (HAARP) observatory. We have adapted Fejer's well-known cross-modulation probing method to determine the extent of ionospheric conductivity modification in the D-region ionosphere with high (5-μsec) time resolution. We demonstrate that the method can be used to analyze D-region conductivity changes produced by HF heating both during the initial stages of heating and under steady-state conditions. The sequence of CW probe pulses used allow the separation of cross-modulation effects that occur as the probe pulse propagates upward and downward through the heated region. We discuss how this probing technique can be applied to benefit ELF/VLF wave generation experiments and ionospheric irregularities experiments at higher altitudes. We demonstrate that large phase changes equivalent to Doppler shift velocities >60 km/sec can be imposed on HF waves propagating through the heated D-region ionosphere.

[1] The contemporary coastal ocean, characterized by abundant nutrients and high primary productivity, is generally seen as a significant CO₂ sink at the global scale. However, mechanistic understanding of the coastal ocean carbon cycle remains limited, leading to the unanswered question of why some coastal systems are sources while others are sinks of atmospheric CO₂. Here we proposed a distinct physical-biogeochemical setting, Ocean-dominated Margin (OceMar), in order for better shaping the concept of the coastal ocean carbon study. OceMars, in contrast to previously recognized River-dominated Ocean Margins (RiOMar), are characterized by dynamic interactions with the open ocean, which may provide non-local CO₂ sources thereby modulating the CO₂ fluxes in OceMars. Using the basin areas of the largest marginal seas of the Pacific and the Atlantic, the South China Sea and the Caribbean Sea as examples of OceMars, we demonstrated that such external CO₂ sources controlled the CO₂ fluxes.

[1] Kawasaki Disease (KD) is the most common cause of acquired heart disease in children worldwide. Recently, a climatological study suggested that KD may be triggered by a windborne agent traveling across the north Pacific through the westerly wind flow prevailing at mid-latitudes. Here we use KD records to describe the association between enhanced disease activity on opposite sides of the basin and different phases of the El Niño-Southern Oscillation (ENSO) phenomenon, via the linkage to these tropospheric winds. Results show that years with higher-than-normal KD cases in Japan preferentially occur during either El Niño Modoki or La Niña conditions, while in San Diego during the mature phase of El Niño or La Niña events. Given that ENSO offers a degree of predictability at lead times of 6 months, these modulations suggest that seasonal predictions of KD could be used to alert clinicians to periods of increased disease activity.

[1] Getting seismic data from the deep oceans usually involves ocean-bottom seismometers, but hydrophone arrays may provide a practical alternative means of obtaining vector data. We here explore this possibility using hydrophone stations of the International Monitoring System (IMS), which have been used to study icebergs and T-wave propagation among others. These stations consist of three hydrophones at about the depth of the deep sound channel in a horizontal triangle array with 2 km sides. We use data from these stations in the very low frequency regime (0.01 - 0.05 Hz band), to demonstrate that these stations can also be used as water column seismometers. By differencing the acoustic pressure, we obtain vector quantities analogous to what a seismometer would record. Comparing processed hydrophone station records of the 2004 Great Sumatra-Andaman Earthquake with broadband seismograms from a nearby island station, we find that the differenced hydrophones are indeed a practical surrogate for seismometers.

[1] Coastal upwelling is typically related to the eastern boundary upwelling system (EBUS), whereas the powerful southwest Asian summer monsoon (ASM) can also generate significant cold, nutrient-rich deep water in western coastal zones. Here we present a sea surface temperature (SST) record (AD 1876-1996) derived from coral Sr/Ca for an upwelling zone in the northern South China Sea (NSCS). The upwelling-induced SST anomaly record reveals prominent multi-decadal variability driven by ASM dynamics with an abrupt transition from warmer to colder conditions in 1930, and a return to warmer conditions after 1960. Previous studies suggest the expected increase in atmospheric CO₂ for the coming decades may result in intensification in the EBUS, which could enhance upwelling of CO₂-rich deep water thus exacerbating the impact of acidification in these productive zones. In contrast, the weakening trend since 1961 in the upwelling time series from the NSCS suggests moderate regional ocean acidification from upwelling thus a stress relief for marine life in this region.

[1] We use satellite observations to show that, between 1992 and 2011, the Pine Island Glacier hinge-line retreated at a rate of0.95 ± 0.09 km yr^-1 despite a progressive steepening and shoaling of the glacier surface and bedrock slopes, respectively, which ought to impede retreat. The retreat has remained constant because the glacier terminus has thinned at an accelerating rate of

[2] 0.53 ± 0.15 m yr^-2, with comparable changes upstream. This acceleration is consistent with an intensification of ocean-driven melting in the cavity beneath the floating section of the glacier. The pattern of hinge-line retreat meanders, and is concentrated in isolated regions until ice becomes locally buoyant. Because the glacier-ocean system does not appear to have reached a position of relative stability, the lower limit of sea level projections may be too conservative.

[1] Determining the bulk composition of island arc lower crust is essential for distinguishing between competing models for arc magmatism and assessing the stability of arc lower crust. We present new constraints on the composition of high P-wave velocity (V_P = 7.3–7.6 km/s) lower crust of the Aleutian arc from best-fitting average lower crustal V_P/V_S ratio using sparse converted S-waves from an along-arc refraction profile. We find a low V_P/V_S of ~1.7–1.75. Using petrologic modeling, we show that no single composition is likely to explain the combination of high V_P and low V_P/V_S. Our preferred explanation is a combination of clinopyroxenite (~50–70%) and alpha-quartz bearing gabbros (~30–50%). This is consistent with Aleutian xenoliths and lower crustal rocks in obducted arcs, and implies that ~30–40% of the full Aleutian crust comprises ultramafic cumulates. These results also suggest that small amounts of quartz can exert a strong influence on V_P/V_S in arc crust.

[1] Extraordinarily strong El Niño events, such as those of 1982/83 and 1997/98, have been poorly predicted by operational seasonal forecasts made before boreal spring, despite significant advances in understanding, improved models, and enhanced observational networks. The Equatorial Atlantic Zonal Mode – a phenomenon similar to El Niño but much weaker and peaking in boreal summer – impacts winds over the Pacific, and hence affects El Niño, and also potentially its predictability. Here we use a climate model to perform a suite of seasonal predictions with and without SST in the Atlantic restored to observations. We show for the first time that knowledge of Equatorial Atlantic sea surface temperature (SST) significantly improves the prediction across boreal spring of major El Niño events and also weaker variability. This is because Atlantic SST acts to modulate El Niño variability, rather than triggering events. Our results suggest that better prediction of major El Niño events might be achieved through model improvement in the Equatorial Atlantic.

[1] Ongoing climate warming in the Arctic will thaw permafrost and remobilize substantial terrestrial OC pools. Around a quarter of northern permafrost OC resides in Siberian Yedoma deposits, the oldest form of permafrost carbon. However, our understanding of the degradation and fate of this ancient OC in coastal and fluvial environments still remains rudimentary. Here, we show that ancient dissolved OC (DOC, >21,000 ¹⁴C yrs), the oldest DOC ever reported, is mobilized in stream waters draining Yedoma outcrops. Furthermore, this DOC is highly biolabile: 34 ± 0.8% was lost during a 14-day incubation under dark, oxygenated conditions at ambient river temperatures. Mixtures of Yedoma stream DOC with main stem river and ocean waters, mimicking in situ mixing processes, also showed high DOC losses (14-day; 17 ± 0.8% to 33 ± 1.0%). This suggests that this exceptionally old DOC is among the most biolabile DOC in any previously reported contemporary river or stream in the Arctic.

[1] Past stratospheric ozone depletion has acted to cool the Earth's surface. As the result of the phase-out of anthropogenic halogenated compounds emissions, stratospheric ozone is projected to recover and its radiative forcing (RF-O₃ ~ -0.05 W/m² presently) might therefore be expected to decay in line with ozone recovery itself. Using results from chemistry-climate models, we find that, although model projections using a standard greenhouse gas scenario broadly agree on the future evolution of global ozone, they strongly disagree on RF-O₃ because of a large model spread in ozone changes in a narrow (several km thick) layer, in the northern lowermost stratosphere. Clearly, future changes in global stratospheric ozone cannot be considered an indicator of its overall RF. The multi-model mean RF-O₃ estimate for 2100 is +0.06 W/m² but with a range such that it could remain negative throughout this century or change sign and reach up to ~0.25 W/m².

[1] A laboratory device, Differential Acoustic Resonance Spectroscopy (DARS), has been developed to investigate the acoustic properties of rock materials below 1 KHz. The device is based on analyzing shifts of resonance frequency of a cavity perturbed by the presence of a small sample. Numerical and experimental studies have previously shown that this technique can be used to estimate the compressibility of samples. In this study, we adopt a nonlinear least-squares whole-curve-fitting inversion approach, which for the first time allows estimation of both the compressibility and density of rock samples. In comparison to previous estimation techniques, this inversion method provides more reliable estimation of rock acoustic properties. This research proves that the DARS laboratory device, in conjunction with the calibration technique proposed herein, is a useful tool to estimate the properties of small rock samples. In addition, the simultaneous estimation of compressibility and density can potentially provide information on porosity and, by extension, a link between porosity and acoustic modulus at low frequency.

[1] The definition and quantification of uncertainty depend on the error model used. For uncertainties in precipitation measurements, two types of error models have been widely adopted: the additive error model and the multiplicative error model. This leads to incompatible specifications of uncertainties and impedes inter-comparison and application. In this letter, we assess the suitability of both models for satellite-based daily precipitation measurements in an effort to clarify the uncertainty representation. Three criteria were employed to evaluate the applicability of either model: 1) better separation of the systematic and random errors; 2) applicability to the large range of variability in daily precipitation; and 3) better predictive skills.

[2] It is found that the multiplicative error model is a much better choice under all three criteria. It extracted the systematic errors more cleanly, was more consistent with the large variability of precipitation measurements, and produced superior predictions of the error characteristics. The additive error model had several weaknesses, such as non-constant variance resulting from systematic errors leaking into random errors, and the lack of prediction capability. Therefore the multiplicative error model is a better choice.

[1] We present an innovative approach to the generation of remotely sensed high-resolution sea surface topography that improves coastal and mesoscale dynamic characterization. This new method is applied for the period 2002-2010 in the northwestern Mediterranean Sea, an area marked by a small Rossby radius. The spectral content of the new mapped data is closer to that of the along-track signal and displays higher levels of energy in the mesoscale bandwidth with the probability distribution of the new velocity fields 30% closer to drifters estimations. The fields yield levels of eddy kinetic energy 25% higher than standard altimetry products, especially over regions regularly impacted by mesoscale instabilities. Moreover, qualitative and quantitative comparisons with drifters, glider and satellite sea surface temperature observations further confirm that the new altimetry product provides, in many cases, a better representation of mesoscale features (more than 25% improvement in correlation with glider data during an experiment).

[1] We performed laboratory laser-induced breakdown spectroscopy (LIBS) and laser Raman spectroscopy measurements on samples from a layered outcrop from the Atacama Desert, Chile. This outcrop is a terrestrial morphological and possibly mineralogical analogue for similar formations that will likely be investigated by the Curiosity rover at Gale Crater. Our results demonstrate that fast LIBS analysis can generate semi-quantitative chemical profiles in sub-minute times using automated data processing tools. Therefore the LIBS instrument can be an invaluable tactical tool on the Curiosity rover for remote, rapid geochemical survey of layered outcrops, thus serving daily operational needs. The derived chemical profiles, supported by the range of minerals identified by Raman spectroscopy, is consistent with the products of a continental evaporitic lake. In the framework of future surface exploration on Mars, a combined Raman/LIBS investigation may provide a rapid mineralogical/chemical evaluation of targets that can be useful for selecting samples to be eventually collected for sample return purposes or for selecting sample sites to be drilled in the search for astrobiology-relevant species.

[1] We provide new insights into the two main seismic events occurred in 2012 in the Emilia region, Italy. We extend the results from previous studies, based on the analytic inversion modeling of GPS and RADARSAT-1 InSAR measurements, by exploiting RADARSAT-2 data. Moreover, we benefit from the available large amounts of geological and geophysical information through a Finite Element Method (FEM) modeling, implemented in a structural mechanical context, to investigate the impact of known buried structures on the modulation of the ground deformation field. We find that the displacement pattern associated with the May 20 event is consistent with the activation of a single fault segment of the Inner Ferrara Thrust, in good agreement with the analytic solution. In contrast, the interpretation of the May 29 episode requires the activation of three different fault segments and a block roto-translation of the Mirandola anticline. The proposed FEM-based methodology is applicable to other seismic areas where the complexity of buried structures is known and it plays a fundamental role in the modulation of the associated surface deformation pattern.

[1] [1] Satellite-derived Moderate-resolution Imaging Spectroradiometer (MODIS) ice-surface temperature (IST) of the Greenland ice sheet shows a positive trend and two major melt events from 2000-present. IST increased by ~0.55 ± 0.44 °C/decade, with the greatest increase (~0.95 ± 0.44 °C/decade) found in northwestern Greenland where coastal temperatures and mass loss are also increasing and outlet glaciers are accelerating. IST shows the highest rates of increase during summer (~1.35 ± 0.47 °C/decade) and winter (~1.30 ± 1.53 °C/decade), followed by spring (~0.60 ± 0.98 °C/decade). In contrast, a decrease in IST was found in the autumn (~-1.49 ± 1.20 °C /decade). The IST trends in this work are not statistically significant with the exception of the trend in northwestern Greenland. Major surface melt (covering 80 percent or more of the ice sheet) occurred during the 2002 and 2012 melt seasons where clear-sky measurements show a maximum melt of ~87 and ~95 percent of the ice sheet surface, respectively. In 2002 most of the extraordinary melt was ephemeral, whereas in 2012 the ice sheet not only experienced more total melt, but melt was more persistent, and the 2012 summer was the warmest in the MODIS record (-6.38 ± 3.98 °C). Our data show that major melt events may not be particularly rare during the present period of ice sheet warming.

[1] Observations from theSMOS satellite are used to reveal new aspects of Tropical Atlantic sea surface salinity (SSS) variability. Over an annual cycle, the variability is dominated by eastern and western basin SSS ‘poles’, with seasonal ranges up to 6.5 pss, that vary out of phase by 6 months and largely compensate each other. A much smaller SSS range (0.08 pss) is observed for the region as a whole. The dominant processes controlling SSS variability are investigated using GPCPv2.2 precipitation (P), OAFlux evaporation (E) and Dai and Trenberth river flow (R) datasets. For the western pole, SSS varies in-phase with P and lags R by 1-2 months; a more complex relationship holds for the eastern pole. The synthesis of novel satellite SSS data with E, P and R enables a new approach to determining variability in Tropical freshwater fluxes and its potential impacts on the Atlantic ocean circulation.

[1] This paper describes initial results from a broad-scale study to assess decadal climate hindcast skills of the HadCM3, GFDL-CM2.1, NCAR-CCSM4, and MIROC5 global Earth System Models (ESMs) in experiments conducted under the Coupled Model Intercomparison Project 5. Analyses of decadal hindcast and simulation experiments using historical aerosol optical depthsshow statistically-significant decadal predictability skill of global-average and tropical sea-surface temperature (SST) anomalies during 1961 to 2010. The skill, however, varies by averaging region and decade. It was also found that volcanic eruptionsinfluence SSTs and are one of the sources of decadal SST hindcast skill. In the actual climate system, however, volcanic eruptions themselves are not predictable and, therefore, their effects on the climate system can only be predictd after eruptions. In the four ESMs utilized in this study, decadal hindcast skills of SST anomalies over ocean-basin size averaging regions generally improve due to model initialization with observed data.

[1] To better understand the physical drivers of submarine groundwater discharge (SGD) in the coastal ocean, we conducted a detailed field and modeling study within an unconfined coastal aquifer system. We monitored the hydraulic gradient across the coastal aquifer and movement of the mixing zone over multiple years. At our study site, sea level dominated over groundwater head as the largest contributor to variability in the hydraulic gradient and therefore SGD. Model results indicate the seawater recirculation component of SGD was enhanced during summer while the terrestrial component dominated during winter due to seasonal changes in sea level driven by a combination of long period solar tides, temperature and winds. In one year, sea level remained elevated year round due to a combination of ENSO and NAO climate modes. Hence, predicted changes in regional climate variability driven sea level may impact future rates of SGD and biogeochemical cycling within coastal aquifers.

[1] A multivariate regression model derived from climate model simulations is shown to produce skillful predictions of unforced, annual mean sea surface temperature variations on multi-year time scales in observations and climate model simulations. Patterns that can be predicted with skill are identified explicitly and shown to arise from a combination of persistence and coupled interactions in the Pacific Ocean. Adding the regression model predictions to an estimate of the response to anthropogenic and natural forcing yields a prediction with higher skill than either alone, demonstrating the contribution of initial condition information to skill on multi-year time scales.

[1] Marine cloud brightening (MCB) is a proposed technique to limit global warming through injections of sea spray into the marine boundary layer. Using the Norwegian Earth System Model, the sensitivity of MCB to sea salt amount and particle size was studied by running a set of simulations in which Aitken (r _e = 0.04 μ m), accumulation (r_e = 0.22 μ m) or coarse (r_e = 2.46 μ m) mode sea salt emissions were increased uniformly by 10 ^− 11 to 10 ^− 8 kg m ^− 2 s ^− 1. As desired, accumulation mode particles had a negative radiative effect of down to -3.3 W m ^− 2. Conversely, for Aitken mode particles, injections of 10 ^− 10 kg m ^− 2 s ^− 1 or greater led to a positive forcing of up to 8.4 W m ^− 2, caused by a strong competition effect combined with the high critical supersaturation of Aitken mode sea salt. The coarse mode particles gave a positive forcing of up to 1.2 W m ^− 2 because of a decrease in activation of background aerosols. Sensitivity experiments show that the competition effect dominated our results. MCB may have a cooling effect, but if the wrong size or injection amount is used, our simulations show a warming effect on the climate system.

[1] Cirrus clouds, thin ice clouds in the upper troposphere, have a net warming effect on Earth's climate. Consequently, a reduction in cirrus cloud amount or optical thickness would cool the climate. Recent research indicates that by seeding cirrus clouds with particles that promote ice nucleation, their lifetimes and coverage could be reduced. We have tested this hypothesis in a global climate model with a state-of-the-art representation of cirrus clouds, and find that cirrus cloud seeding has thepotential to cancel the entire warming caused by human activity from pre-industrial times to present day. However, the desired effect is only obtained for seeding particle concentrations that lie within an optimal range. With lower than optimal particle concentrations a seeding exercise would have no effect. Moreover, a higher than optimal concentration results in an over-seeding that could have the deleterious effect of prolonging cirrus lifetime and contributing to global warming.

[2] with global coverage. In the Northern Hemisphere, the January SPE started at the end of a polar stratospheric warming period. The SPE effect is superimposed by large-scale subsidence of mesospheric NO_x-rich air, which partly masks direct chemical SPE effects. SPE-induced NO_x increases by 5, 20, 50 and 100 ppbv at altitudes of 50, 57, 60 and 70 km, respectively, are observed during the January SPE, and by 2, 5, 10, 20, 30, and 35 ppbv at altitudes of 47, 50, 53, 60, 63 and 66 km, respectively, during the March SPE. SPE-related ozone loss is clearly observed in the mesosphere, particularly in the tertiary ozone maximum. A sudden short-term HNO₄ increase immediately after the January SPE hints at SPE-triggered HO_x chemistry. In the Southern Hemisphere, a large NO_x response is observed (increases by 2, 5, 10, 20, and 30 ppbv at 52, 56, 59, 63 and 70 km in January and 2, 5, 10, 20, 30, 35 ppbv at 47, 50, 53, 60, 63 and 66 km in March), while the effect on other species seems much less pronounced than in the Northern Hemisphere. SPE-related destruction of mesospheric ozone in the Southern Hemisphere was much more pronounced after the March SPE than the January SPE but in both cases ozone recovered within about a day.

[1] Mantle xenoliths provide our clearest look at the magnetic mineral assemblages below the Earth's crust. Previous investigations of mantle xenoliths suggested the absence of magnetite and metals, and proposed that even if such minerals were present, they would be above their Curie temperatures at mantle conditions. Here we use magnetic measurements to examine four exceptionally fresh suites of xenoliths, and show that magnetite occurs systematically, albeit in variable amounts depending on the tectonic setting. Specimens from low geotherm regions hold the largest magnetic remanence. Petrographic evidence shows that this magnetite did not form through serpentinization or other alteration processes. Magnetite, which is generally stable at the P-T-fO₂ conditions in the uppermost mantle, had to have formed either in the mantle or, less likely, in the volcanic conduit. In some cases, the source of the xenoliths was at temperatures <600 °C, which may have allowed this portion of the lithospheric mantle to carry a magnetic remanence. Whether such magnetite carries a remanent magnetization or is simply the source of a strong induced magnetization, these new results suggest that the concept of the Moho as a major magnetic boundary needs to be revisited.

We investigate the changes of the Kuroshio Current in the East China Sea during the last glacial maximum, based on numerical experiments using an ocean model and geochemical analyses of marine sediments. Our numerical experimental results indicate that there was little effect of sea level change on the path of the Kuroshio during the glacial period. Geochemical proxy records of marine sediment cores recovered from inside and outside the Okinawa Trough (OT) show no significant difference in glacial sea surface temperature and planktonic foraminiferal ¹⁸O between the OT and the Ryukyu forearc. This indicates that glacial sea surface temperature and salinity were almost the same inside and outside the OT. Hence, during the glacial Kuroshio water most likely intruded into the OT and flowed along the shelf break until it drained out through the Tokara Strait. © 2013 American Geophysical Union. All rights reserved.

[1] Several tens of thousands of temperature profiles are used to investigate the thermal evolution of the cold wake of Typhoon Fanapi, 2010. Typhoon Fanapi formed a cold wake in the Western North Pacific Ocean on 18 September characterized by a mixed layer that was >2.5 °C cooler than surrounding water, and extending to >80 m, twice as deep as the pre-existing mixed layer. The initial cold wake became capped after 4 days as a warm, thin surface layer formed. The thickness of the capped wake, defined as the 26 °C to 27 °C layer, decreased, approaching the background thickness of this layer with an e-folding time of 23 days, almost twice the e-folding lifetime of the Sea Surface Temperature (SST) cold wake (12 days). The wake was advected several hundreds of kilometers from the storm track by a pre-existing mesoscale eddy. The observations reveal new intricacies of cold wake evolution and demonstrate the challenges of describing the thermal structure of the upper ocean using sea surface information alone. © 2013 American Geophysical Union. All rights reserved.

[1] Recent work comparing historical hydrographic data with modern Argo observations shows a long-term change in the global ocean temperature. The magnitude of this change is greater than estimates of late 20^th century warming, and implies a century-scale change in the global oceans. Using global coupled climate models from the Coupled Model Intercomparison Project Phase 5 suite of simulations, we assess to what extent this observed temperature difference can be attributed to a genuine long-term warming trend. After accounting for natural variability and sampling errors, we find convincing evidence that there has indeed been a century-scale anthropogenic warming of the global ocean up to the present day, and a strong possibility of anthropogenic warming from 1873 to 1955. The estimated 1873–1955 ocean warming implies a net top-of-atmosphere energy imbalance of 0.1 ± 0.06 Wm^–2, and a thermosteric global mean sea level rise of 0.50 ± 0.2 mma^–1.

[1] The observed rapid loss of thick multiyear sea ice over the last 7 years and the September 2012 Arctic sea ice extent reduction of 49% relative to the 1979–2000 climatology are inconsistent with projections of a nearly sea ice-free summer Arctic from model estimates of 2070 and beyond made just a few years ago. Three recent approaches to predictions in the scientific literature are as follows: (1) extrapolation of sea ice volume data, (2) assuming several more rapid loss events such as 2007 and 2012, and (3) climate model projections. Time horizons for a nearly sea ice-free summer for these three approaches are roughly 2020 or earlier, 2030 ± 10 years, and 2040 or later. Loss estimates from models are based on a subset of the most rapid ensemble members. It is not possible to clearly choose one approach over another as this depends on the relative weights given to data versus models. Observations and citations support the conclusion that most global climate model results in the CMIP5 archive are too conservative in their sea ice projections. Recent data and expert opinion should be considered in addition to model results to advance the very likely timing for future sea ice loss to the first half of the 21st century, with a possibility of major loss within a decade or two.

[1] We explore two principal areas of uncertainty associated with paleoclimate reconstructions from speleothem δ¹⁸O (δ¹⁸O_spel): potential non-stationarity in relationships between local climate and larger-scale atmospheric circulation, and routing of water through the karst aquifer. Using a δ¹⁸O_spel record from Turkey, the CSIRO Mk3L climate system model and the KarstFOR karst hydrology model, we confirm the stationarity of relationships between cool season precipitation and regional circulation dynamics associated with the North Sea-Caspian pattern since 1 ka. Stalagmite δ¹⁸O is predicted for the last 500 years, using precipitation and temperature output from the CSIRO Mk3L model and synthetic δ¹⁸O of precipitation as inputs for the KarstFOR model. Interannual variability in the δ¹⁸O_spel record is captured by KarstFOR, but we cannot reproduce the isotopically lighter conditions of the sixteenth to seventeenth centuries. We argue that forward models of paleoclimate proxies (such as KarstFOR) embedded within isotope-enabled general circulation models are now required.

[1] This study applies the C4.5 algorithm to classify tropical cyclone (TC) intensity change in the western North Pacific. The 24 h change in TC intensity (i.e., intensifying and weakening) is regarded as a binary classification problem. A decision tree, with three variables and five leaf nodes, is built by the C4.5 algorithm. The variables include intensification potential (maximum potential intensity minus current intensity), previous 12 h intensity change, and zonal wind shear. All five rules, discovered from the tree by forming a path from the root node to each leaf node, can be interpreted by theories on TC intensification. Data mining results identify a predictor set (i.e., the mined rules) with high classification accuracy. The present study suggests that this data mining approach can shed some light on investigating TC intensity change processes and therefore has the potential to improve the forecasting of TC intensity.

[1] In this study, uncoupled atmospheric general circulation model experiments are conducted to examine the sensitivity of tropical Ocean basins from the Indian Ocean to the tropical Pacific Ocean on the summer precipitation variability over East Asia. It is remarkable that the Indian Ocean basin sea surface temperature (SST) and the tropical Pacific basin SST act on summer precipitation variability over Northeast Asia and southern China quite differently. That is, SST warming in the Indian Ocean largely contributes to the increase in the amount of summer precipitation over East Asia, which is in contrast to the warming of the western tropical Pacific Ocean. Our further analysis indicates that an altered large-scale atmospheric circulation over the western tropical Pacific contributes to contrasting atmospheric motion over East Asia due to the tropics-East Asia teleconnections, which results in changes in the amount of summer precipitation due to the warming of the Indian and western tropical Pacific Oceans.

[1] The hysteresis effect in diurnal cycles of net radiation R_n and ground heat flux G₀ has been observed in many studies, while the governing mechanism remains vague. In this study, we link the phenomenology of hysteresis loops to the wave phase difference between the diurnal evolutions of various terms in the surface energy balance. R_n and G₀ are parameterized with the incoming solar radiation and the surface temperature as two control parameters of the surface energy partitioning. The theoretical analysis shows that the vertical water flux W and the scaled ratio (net shortwave radiation to outgoing longwave radiation) play crucial roles in shaping hysteresis loops of R_n and G₀. Comparisons to field measurements indicate that hysteresis loops for different land covers can be well captured by the theoretical model, which is also consistent with Camuffo-Bernadi formula. This study provides insight into the surface partitioning and temporal evolution of the energy budget at the land surface.

[1] Newly obtained high-resolution seismic data reveal the detailed structure of the Japan Trench axis off Miyagi, Japan, in the region of large shallow slip during the 11 March 2011 M9 Tohoku earthquake. Correlation of seismic images with previous drilling results identifies a possible basal chert-rich layer and hemipelagic/pelagic mudstones overlying igneous Pacific crust. Mapping of acoustic basement depicts the subduction of horst-and-graben topography. The basement and basal chert are subducted beneath a seismically chaotic frontal prism, but the majority of overlying hemipelagic mudstones is offscraped and imbricated at the trench axis as a result of plate boundary compression. A possible décollement is imaged as a seaward dipping reflection at landward part of the trench graben and was likely generated by loading and failure of underthrust sediments. Collectively, these analyses provide a structural framework for understanding sedimentary inputs and the localization of shallow plate boundary slip at the Japan Trench.

[1] In November 2011, the partial pressures of carbon dioxide (pCO₂) in water and air in a floodplain lake of the Amazon River in Brazil were 800 ± 75 and 387 ± 8 ppmv, respectively. Turbulent CO₂ fluxes from the lake measured with eddy covariance ranged from 0.05 to 2.2 µmol m⁻² s⁻¹. The corresponding gas transfer velocities k₆₀₀ ranged from 1.3 to 31.6 cm h⁻¹, averaging 12.2 ± 6.7 cm h⁻¹. At moderate to high wind speed, k₆₀₀ increased with wind speed, with values above parameterizations for other lake ecosystems. During the prevailing tropical low wind speed (below 2.7 m s⁻¹) and high insolation conditions, unexpected high k₆₀₀ values (up to 20 cm h⁻¹) were obtained and correlated with latent heat and sensible heat fluxes. In Amazonian open lakes, owing to long quiescent periods of low wind speed but extremely high daytime insolation and heat fluxes, thermal enhancement makes time-integrated gas transfer velocities four to five times higher than those computed from classic wind parameterization.

[1] Timely and accurate forecasts of tropical cyclones (TCs, i.e., hurricanes and typhoons) are of great importance for risk mitigation. Although in the past two decades there has been steady improvement in track prediction, improvement on intensity prediction is still highly challenging. Cooling of the upper ocean by TC-induced mixing is an important process that impacts TC intensity. Based on detail in situ air-deployed ocean and atmospheric measurement pairs collected during the Impact of Typhoons on the Ocean in the Pacific (ITOP) field campaign, we modify the widely used Sea Surface Temperature Potential Intensity (SST_PI) index by including information from the subsurface ocean temperature profile to form a new Ocean coupling Potential Intensity (OC_PI) index. Using OC_PI as a TC maximum intensity predictor and applied to a 14 year (1998–2011) western North Pacific TC archive, OC_PI reduces SST_PI-based overestimation of archived maximum intensity by more than 50% and increases the correlation of maximum intensity estimation from r² = 0.08 to 0.31. For slow-moving TCs that cause the greatest cooling, r² increases to 0.56 and the root-mean square error in maximum intensity is 11 m s⁻¹. As OC_PI can more realistically characterize the ocean contribution to TC intensity, it thus serves as an effective new index to improve estimation and prediction of TC maximum intensity.

[1] We experimentally investigated the solar wind interaction with moderate-strength lunar magnetic anomalies in which the electrons are magnetized but the ions remain unmagnetized. Previously, we studied the plasma sheaths above an insulating surface in a magnetic dipole field oriented parallel to the surface. In this paper, when the dipole field is oriented normal to the surface, the surface potential largely rises, and a potential bump forms in the sheath in the magnetic cusp region due to a significant magnetic mirror reflection of the electrons. It is also found that the electrons are shielded from the central dipole wings and diverted into the side of the wings. When the dipole field obliquely intersects the surface, an asymmetric potential distribution develops. Our experimental results indicate that lunar surface charging can be greatly modified in the magnetic anomaly regions, creating extreme local electrical environments.

[1] Climate-model simulations of the large-scale temperature responses to increased radiative forcing include enhanced land-sea contrast, stronger response at higher latitudes than in the tropics, and differential responses in warm and cool season climates to uniform forcing. Here we show that these patterns are also characteristic of model simulations of past climates. The differences in the responses over land as opposed to over the ocean, between high and low latitudes, and between summer and winter are remarkably consistent (proportional and nearly linear) across simulations of both cold and warm climates. Similar patterns also appear in historical observations and paleoclimatic reconstructions, implying that such responses are characteristic features of the climate system and not simple model artifacts, thereby increasing our confidence in the ability of climate models to correctly simulate different climatic states.

[1] Since the 1980s, a dramatic downward trend in North African dustiness and transport to the tropical Atlantic Ocean has been observed by different data sets and methods. The precise causes of this trend have previously been difficult to understand, partly due to the sparse observational record. Here we show that a decrease in surface wind speeds associated with increased roughness due to more vegetation in the Sahel is the most likely cause of the observed drop in dust emission. Associated changes in turbulence and evapotranspiration, and changes in large-scale circulation, are secondary contributors. Past work has tried to explain negative correlations between North African dust and precipitation through impacts on emission thresholds due to changes in soil moisture and vegetation cover. The use of novel diagnostic tools applied here to long-term surface observations suggests that this is not the dominating effect. Our results are consistent with a recently observed global decrease in surface wind speed, known as “stilling”, and demonstrate the importance of representing vegetation-related roughness changes in models. They also offer a new mechanism of how land-use change and agriculture can impact the Sahelian climate.

[1] A future Maunder Minimum type grand solar minimum, with total solar irradiance reduced by 0.25% over a 50 year period from 2020 to 2070, is imposed in a future climate change scenario experiment (RCP4.5) using, for the first time, a global coupled climate model that includes ozone chemistry and resolved stratospheric dynamics (Whole Atmosphere Community Climate Model). This model has been shown to simulate two amplifying mechanisms that produce regional signals of decadal climate variability comparable to observations, and thus is considered a credible tool to simulate the Sun's effects on Earth's climate. After the initial decrease of solar radiation in 2020, globally averaged surface air temperature cools relative to the reference simulation by up to several tenths of a degree Centigrade. By the end of the grand solar minimum in 2070, the warming nearly catches up to the reference simulation. Thus, a future grand solar minimum could slow down but not stop global warming.

[1] We analyze seismic waveforms from deep-focus earthquakes occurring in the subducting slab beneath Japan, recorded by broadband ocean bottom seismometers (BBOBSs) installed on the northwestern Pacific Ocean seafloor. The data reveal waveforms with a low-frequency direct P onset, followed by large-amplitude, high-frequency, long-duration Po and So waves. From the analysis of the BBOBS records and a numerical finite-difference method simulation of seismic wave propagation, we elucidate the generation and propagation processes of such guided waves. We demonstrate that the low-frequency direct P and S waves propagate in the asthenosphere and that the following high-frequency, long-duration Po and So waves are developed by multiple forward scattering of P and S waves. The scattering occurs due to laterally elongated heterogeneities in both the subducting and horizontal parts of the oceanic lithosphere, with the apparent velocities (V_p = 8.1 km/s, V_s = 4.6 km/s) being close to the velocities of oceanic lithosphere.

[1] Ultraslow spreading mid-ocean ridges have a low magma budget and melt is distributed unevenly along the ridge axis. There is little or no basaltic crust between isolated magmatic centers. The processes that focus melts to segments of robust magmatism are not yet understood. During a seismic survey of the ultraslow spreading Knipovich Ridge in the Norwegian-Greenland Sea with ocean bottom seismometers, we discovered a seismic gap in the upper mantle beneath Logachev Seamount, where micro-earthquakes clearly delineate a shallowing of the maximum depth of faulting. A topography of the lithosphere that allows melts to travel laterally along its base and rise in areas of thin lithosphere has been proposed as a possible mechanism to explain the focusing of melts at volcanic centers, but has never been confirmed observationally. Our results are the first geophysical evidence for an along-axis variation of the lithospheric thickness at an ultraslow spreading ridge.

[1] We used a first-order, monthly snow model and observations to disentangle seasonal influences on 20th century,regional snowpack anomalies in the Rocky Mountains of western North America, where interannual variations in cool-season (November–March) temperatures are broadly synchronous, but precipitation is typically antiphased north to south and uncorrelated with temperature. Over the previous eight centuries, regional snowpack variability exhibits strong, decadally persistent north-south (N-S) antiphasing of snowpack anomalies. Contrary to the normal regional antiphasing, two intervals of spatially synchronized snow deficits were identified. Snow deficits shown during the 1930s were synchronized north-south by low cool-season precipitation, with spring warming (February–March) since the 1980s driving the majority of the recent synchronous snow declines, especially across the low to middle elevations. Spring warming strongly influenced low snowpacks in the north after 1958, but not in the south until after 1980. The post-1980, synchronous snow decline reduced snow cover at low to middle elevations by ~20% and partly explains earlier and reduced streamflow and both longer and more active fire seasons. Climatologies of Rocky Mountain snowpack are shown to be seasonally and regionally complex, with Pacific decadal variability positively reinforcing the anthropogenic warming trend.

[1] The role of planetary waves in causing stratospheric sudden warmings (SSWs) is well understood and quantified. However, recent studies have indicated that secondary planetary waves are excited in the mesosphere and lower thermosphere following SSWs. We use a version of the Whole Atmosphere Community Climate Model constrained by reanalysis data below 50 km to simulate the SSW of January 2012, a minor warming followed by the formation of an elevated stratopause. We document the occurrence of enhanced Eliassen-Palm flux divergence in the mesosphere and lower thermosphere associated with faster, secondary westward-propagating planetary waves of wave number 1 and period <10 days. We confirm the presence of these secondary planetary waves using observations made by the Sounding of the Atmosphere using the Broadband Emission Radiometry instrument onboard NASA's Thermosphere-Ionosphere-Mesosphere Energetics and Dynamics satellite.

[1] At the Voyager 1 (V1) spacecraft in the outer heliosphere, the intensities of both anomalous cosmic rays and galactic cosmic rays (GCRs) changed suddenly and decisively on 25 August (121.7 AU from the Sun). Within a matter of a few days, the intensity of 1.9–2.7 MeV protons and helium nuclei had decreased to less than 0.1 of their previous value, and eventually the intensities decreased by factors of at least 300–500. Also, on 25 August, the GCR protons, helium, and electrons increased suddenly in just 2 or 3 days by a factor of up to 2. The intensities of the GCR nuclei of all energies from 2 to 400 MeV then remained essentially constant with intensity levels and spectra that may represent the local GCR. The suddenness of these intensity changes indicates that V1 has crossed a well-defined boundary for energetic particles at this time possibly related to the heliopause.

[1] The diverse and fundamental effects that aeolian processes have on the biosphere and geosphere are commonly generated by horizontal sediment transport at the land surface. However, predicting horizontal sediment transport depends on vegetation architecture, which is difficult to quantify in a rapid but accurate manner. We demonstrate an approach to measure vegetation canopy architecture at high resolution using lidar along a gradient of dryland sites ranging from 2% to 73% woody plant canopy cover. Lidar-derived canopy height, distance (gaps) between vegetation elements (e.g., trunks, limbs, leaves), and the distribution of gaps scaled by vegetation height were correlated with canopy cover and highlight potentially improved horizontal dust flux estimation than with cover alone. Employing lidar to estimate detailed vegetation canopy architecture offers promise for improved predictions of horizontal sediment transport across heterogeneous plant assemblages.

[1] We investigate the dependence of the O⁺ escape rate on the upstream interplanetary magnetic field (IMF) direction by using data from the Analyser of Space Plasma and Energetic Atoms (ASPERA-4) instrument and the magnetometer (MAG) onboard Venus Express. We consider two cases, namely the perpendicular IMF case (167 events) and the parallel IMF case (82 events), where IMF is nearly perpendicular to the Venus-Sun line and nearly parallel to it. By integrating O⁺ fluxes observed on the nightside, total O⁺ escape rates of (5.8 ± 2.9) × 10²⁴ s⁻¹ (perpendicular IMF case) and (4.9 ± 2.2) × 10²⁴ s⁻¹ (parallel IMF case) are obtained. As these values are not significantly different, the upstream IMF direction does not affect the total amount of O⁺ outflow from Venus. The different acceleration mechanisms must balance each other in order to keep the escape rate the same.

[1] We use a very high resolution global climate model (~25 km grid size) with prescribed sea surface temperatures to show that greenhouse warming enhances the occurrence of hurricane-force (> 32.6 m s^–1) storms over western Europe during early autumn (August–October), the majority of which originate as a tropical cyclone. The rise in Atlantic tropical sea surface temperatures extends eastward the breeding ground of tropical cyclones, yielding more frequent and intense hurricanes following pathways directed toward Europe. En route they transform into extratropical depressions and reintensify after merging with the midlatitude baroclinic unstable flow. Our model simulations clearly show that future tropical cyclones are more prone to hit western Europe, and do so earlier in the season, thereby increasing the frequency and impact of hurricane force winds.

[1] A high-resolution marine record from the northern Norwegian continental margin off Lofoten is used to reconstruct changes in the oceanography of the Nordic seas during marine isotope stage (MIS) 2 including the Last Glacial Maximum and early deglaciation circa 25 to 16 ka. The period was characterized by generally warm subsurface water temperatures >2°C and inflow of Atlantic surface water. Several events were characterized by decrease in ventilation of the intermediate water and low subsurface temperature and salinity. They correlate with colder atmospheric temperatures as seen in ice cores. The events terminated with gradual strengthening of the intermediate water ventilation and increase in subsurface temperature. The generation of intermediate water was unstable and experienced climate and ventilation changes on millennial and centennial timescales. The changes appear consistent with modeling experiments that predict short-lasting circulation stops during MIS 2 due to release of meltwater in the Nordic seas.

[1] Continued anthropogenic CO₂ emissions are expected to impact tropical coral reefs by further raising sea surface temperatures (SST) and intensifying ocean acidification (OA). Although geoengineering by means of solar radiation management (SRM) may mitigate temperature increases, OA will persist, raising important questions regarding the impact of different stressor combinations. We apply statistical Bioclimatic Envelope Models to project changes in shallow water tropical coral reef habitat as a single niche (without resolving biodiversity or community composition) under various representative concentration pathway and SRM scenarios, until 2070. We predict substantial reductions in habitat suitability centered on the Indo-Pacific Warm Pool under net anthropogenic radiative forcing of ≥3.0 W/m². The near-term dominant risk to coral reefs is increasing SSTs; below 3 W/m² reasonably favorable conditions are maintained, even when achieved by SRM with persisting OA. “Optimal” mitigation occurs at 1.5 W/m² because tropical SSTs overcool in a fully geoengineered (i.e., preindustrial global mean temperature) world.

[1] Deep current meter data and output from two high-resolution global ocean circulation models are used to determine the prevalence and location of strong bottom currents in the greater Agulhas Current system. The two models and current meter data are remarkably consistent, showing that benthic storms, with bottom currents greater than 0.2 m s⁻¹, occur throughout the Agulhas retroflection region south of Africa more than 20% of the time. Furthermore, beneath the mean Agulhas Current core and the retroflection front, bottom currents exceed 0.2 m s⁻¹ more than 50% of the time, while away from strong surface currents, bottom currents rarely exceed 0.2 m s⁻¹. Implications for sediment transport are discussed and the results are compared to atmospheric storms. Benthic storms of this strength (0.2 m s⁻¹) are comparable to a 9 m s⁻¹ (Beaufort 5) windstorm, but scaling shows that benthic storms may be less effective at lifting and transporting sediment than dust storms.

[1] The evolution of atmospheric composition downwind of a city depends strongly on the concentration of OH within the plume. We use space-based observations of NO₂, a molecule that affects both the sources and sinks of OH, to examine the functional dependence of OH concentration on the speed of the wind over Riyadh, Saudi Arabia. These observations illustrate the nonlinear dependence of the OH concentration on NO₂ and on the rate of atmospheric mixing. We derive a range of NO_x lifetimes of 5.5–8.0 h, lifetimes that correspond to an effective plume-averaged OH concentration of 7.6 × 10⁶ molecules cm^–3 at fast (26 km h^–1) and 5.2 × 10⁶ molecules cm^–3 at slow (4 km h^–1) wind speeds.

[1] The elusive nature of the post-2004 upper ocean warming has exposed uncertainties in the ocean's role in the Earth's energy budget and transient climate sensitivity. Here we present the time evolution of the global ocean heat content for 1958 through 2009 from a new observation-based reanalysis of the ocean. Volcanic eruptions and El Niño events are identified as sharp cooling events punctuating a long-term ocean warming trend, while heating continues during the recent upper-ocean-warming hiatus, but the heat is absorbed in the deeper ocean. In the last decade, about 30% of the warming has occurred below 700 m, contributing significantly to an acceleration of the warming trend. The warming below 700 m remains even when the Argo observing system is withdrawn although the trends are reduced. Sensitivity experiments illustrate that surface wind variability is largely responsible for the changing ocean heat vertical distribution.

[1] Surface waters in upwelling regions are thought to be nutrient rich and hence inhibit nitrogen fixation (diazotrophy) because diazotrophs can preferentially assimilate nitrate and ammonia instead of expending energy to fix dinitrogen. We found average nitrogen fixation rates to be two to seven times higher in the surface waters of the upwelling region of the eastern equatorial Atlantic than typically measured here during non-upwelling periods. We posit that in this region, low nitrate-phosphate ratio waters are upwelled, and an initial bloom of non-diazotrophic phytoplankton removes recently upwelled nitrate. Thereby, diazotrophy is fuelled by residual phosphate and by a combination of aeolian and upwelled sources of iron. Annually, we estimate that approximately 47 Gmol of new nitrogen is introduced by diazotrophy in upwelled waters alone and 195 Gmol N is fixed in the equatorial Atlantic region. Our findings challenge the paradigm that the highest nitrogen fixation rates occur in oligotrophic gyres and instead provide evidence of its importance in upwelling regimes where phosphate- and iron-rich waters rich are upwelled.

[1] Subduction is a fundamental Earth process, yet many aspects of subduction systems remain to be fully understood. Here we present anisotropic receiver function (RF) analysis to characterize the structure of the mantle wedge beneath the Ryukyu subduction zone. Radial and transverse P-to-S RFs computed for eight broadband stations yield evidence for coherent P-to-SV conversions originating at the top of the subducting slab. We also observe conversions on the transverse component RFs that are consistent with the presence of multiple anisotropic layers, with structure varying significantly along strike. Forward modeling of observations at station ZMM in the center of the Ryukyu arc yields evidence for a ~6 km thick layer of strongly anisotropic material, most likely serpentinite, directly above the subducting slab and likely B-type olivine fabric in the shallow mantle wedge.

[1] Predicting the West African monsoon (WAM) remains a major challenge for weather and climate models. We compare multiday continental-scale simulations of the WAM that explicitly resolve moist convection with simulations which parameterize convection. Simulations with the same grid spacing but differing representations of convection isolate the impact of the representation of convection. The more realistic explicit convection gives greater latent and radiative heating farther north, with latent heating later in the day. This weakens the Sahel-Sahara pressure gradient and the monsoon flow, delaying its diurnal cycle and changing interactions between the monsoon and boundary layer convection. In explicit runs, cold storm outflows provide a significant component of the monsoon flux. In an operational global model, biases resemble those in our parameterized case. Improved parameterizations of convection that better capture storm structures, their diurnal cycle, and rainfall intensities will therefore substantially improve predictions of the WAM and coupled aspects of the Earth system.

[1] In this work, we map and develop for the first time an independent satellite constrained NO_x emission inventory for India for 2005 using an inverse technique and iterative procedure. We used OMI tropospheric NO₂ column retrievals over the Indian region, with tropospheric NO₂ columns simulated by the WRF-Chem model using the INTEX-B emission inventory. We determined the local relationship between modeled emissions and tropospheric columns and iteratively apply this relationship to OMI observations to derive an optimized NOx emission inventory on a 0.5° × 0.5° grid. The optimized total NO_x emissions for India amount to 1.9 TgN/y and agree within 25% with EDGARv4.1 and the INTEX-B estimate. Our top-down inventory captures many of the missing hotspots in the original inventory and suggests that the INTEX-B inventory overestimates emissions over the Western and Eastern Indo-Gangetic region and underestimates point sources. We further evaluate the effect of the top-down inventory on surface ozone, which clearly indicates significant changes in spatial distribution.