This section discusses comparisons with the data over Australia between 2005 and 2009. A broader, more detailed evaluation of the model can be found in Appendix A, where the model is compared to ground-based flask measurements of surface concentration, aircraft-borne measurements of the upper troposphere from Civil Aircraft for the Regular Investigation of the Atmosphere Based on an Instrument Container (CARIBIC) flights, and satellite-borne measurements of the stratosphere from the Halogen Occultation Experiment (HALOE) instrument. For each comparison the model is sampled at the same location and time as the measurement.
7.1. Surface Concentrations at Flask and AGAGE Sites
 Figures 6 and 7 show the model and measurements of surface methane at Cape Ferguson and Cape Grim, respectively. The model output is shown both with and without NEWWET. At Cape Ferguson, surface winds are generally from the east, as discussed in section 3, so the measurements reflect clean air from the Pacific Ocean. When the winds are from the west, continental air is sampled and the concentrations are higher. The surface concentration from the model run with NEWWET is up to 3 ppb larger than the model run without, and increase the model concentration by less than the error bars of the measurements. The seasonal variation of the surface concentration is well described by the model: the correlation coefficient (r2) is 0.75 with NEWWET and 0.74 without. The average difference between the data and the model with NEWWET is 3.6 ± 6.9 ppb (0.20%) (mean ± one standard deviation); without NEWWET the average difference is 4.8 ± 6.7 ppb (0.27%).
Figure 6. (a) Model and observed weekly methane surface concentrations (ppb) at Cape Ferguson (19.3°S, 147.1°E) between 2005–2008. Model results are shown with and without NEWWET. (b) Difference between observed and model concentrations. (c) Monthly mean tracer results for the 13 geographical regions. The horizontal resolution of GEOS-Chem is 2° × 2.5°. The model was sampled at the location and time of the measurements.
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Figure 7. As Figure 6, but for Cape Grim (40.7°S, 144.7°E) and with daily resolution. (a and b) The symbols are daily-averaged measurements while the solid lines are 7-d running means.
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 For Cape Grim, NEWWET makes very little difference, as expected for a measurement site so far from these revised emissions. The concentrations generally reflect clean atmosphere values of methane. When the winds are from the east or north, higher concentrations reflect local emissions from Tasmania and transport in from other regions of Australia, respectively. Figure 7a shows that the model reproduces the background concentrations well, but has difficulty reproducing concentrations influenced by local sources: the model both underestimates and overestimates these elevated events. The mean difference between the data and the model is 3.1 ± 8.4 ppb (0.15%) with a correlation coefficient of 0.74.
 At both sites, the model slightly overestimates the growth rate of methane. There is a trend of −2 ppb/year in the difference between the data and the model. A similar trend is seen at other surface flask sites (see Appendix A). The trend is likely due to an overestimation in the increase of anthropogenic emissions in the model.
 Figures 6 and 7 also show the monthly mean contribution to surface concentration above background from the geographic tagged tracers with NEWWET. As discussed in section 5, the tagged tracers were set to zero at the beginning of each month with previous monthly contributions subsumed by the background tracer. Figure 8 shows the monthly-averaged contributions to the surface concentration above background from the different sources for the four Australian regions from the tagged tracer run for 2008.
Figure 8. Model monthly averaged contribution to the surface concentration from tagged sources for Darwin, Cape Ferguson, Wollongong, and Cape Grim. From left to right the columns show contributions from West Tropical Australia (WTA), East Tropical Australia (ETA), Desert Australia, and Metropolitan Australia. Note the different y-axis scales for the different sites. Permanent and seasonal wetlands are NEWWET emissions in northern Australia, while wetlands are located mainly in the southeast of the country.
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 At Cape Ferguson, the change to the surface concentration above background is about equally influenced by local emissions (25–60%) and transport from the Metropolitan Australian region to the south (10–60%). The local emissions are from oceans, NEWWET, animals, and coal. These sources are constant throughout the year with the exception of the seasonal wetlands, which are strongest in the summer. Emissions from Metropolitan Australia are dominated by coal and animals and their influence at Cape Ferguson is largest in the autumn and winter, reflecting general circulation patterns (section 3). The relative contribution of the sources is similar from year to year (not shown), except in the case of seasonal wetlands, which are much stronger in 2006 and 2008. Transport from South America and Africa is the largest intercontinental contribution, the effects of which peak in the winter and early spring. There is also transport from Southeast Asia and the Southern Hemisphere tropics in the summer, with the largest effect in 2008 (5 ppb).
 At Cape Grim, local emissions from animals, landfills, and wetlands (located in southern Victoria and South Australia) are the largest contributors to changes in the surface concentrations above background (75–95%). Contributions from biomass burning are largest in the autumn, while contributions from wetlands are largest in the summer and autumn (December–June). There is interannual variability in contributions from biomass burning, which is largest in 2007, and wetlands, which are largest in 2005. The spike in the tracers in late 2006/early 2007 is caused by a large biomass burning event, where large methane values are seen in the model but are not observed in the data. Transport into the region from overseas is primarily from South America and Africa and is strongest in the winter and spring, similar to Cape Ferguson.
7.2. XCH4 at TCCON Sites
 Figure 9 shows the model and measured XCH4 at Wollongong. Including wetlands emissions from northern Australia makes very little difference to the columns, as expected. The TCCON instrument at Wollongong began operating in 2008, so the record is not as long as for the surface sites. The model and data agree well: the mean difference between the data and the model is 7.1 ± 8.4 ppb (0.40%) and a correlation coefficient of 0.60. These comparisons are consistent with the model comparison of surface concentration comparisons at Cape Ferguson and Cape Grim.
Figure 9. (a) Model and TCCON total column daily methane at Wollongong (34.4°S, 150.9°E). The two model results are with and without the new wetland emissions. (b) Difference between TCCON measurements and model output. The symbols represent the daily averaged measurements while the solid lines represent a 7-d running mean. (c) Monthly mean tracer results.
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 Figure 9c shows the monthly mean tracer results for the total column above background at Wollongong. The XCH4 is dominated by emissions from the Metropolitan Australian region. Figure 8 shows that at the surface emissions from coal mining are the dominant contribution to the change in concentration above background (90–95%), with only small contributions from animals, landfills, and biomass burning. Transport from South America, strongest in winter and spring, is the second largest source of additional methane above background at Wollongong.
 Figure 10 shows the XCH4 at Darwin. The difference between the model run with and without NEWWET is up to 8 ppb and is largest in the summer when the seasonal wetlands are active. However, the prevailing winds at this time of year are from the north and west, while the bulk of the seasonal wetlands lie to the south, so it is not expected that NEWWET will have a great effect at Darwin. The blue shaded regions indicate periods when Darwin is located in the meteorological northern hemisphere. A GEOS-Chem simulation of an idealized inert tracer was used to determine the position of the chemical gradient formed due to the ITCZ associated circulation; this is further discussed in Appendix B. The mean difference between the data and the model is 15.9 ± 7.5 ppb (0.91%) with NEWWET and 17.4 ± 7.2 ppb (0.99%) without.
Figure 10. As Figure 9, but for Darwin (12.4°S, 130.9°E). The blue shaded regions represent times when Darwin is in the chemical Northern Hemisphere (see text).
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 During the periods when Darwin is in the chemical Northern Hemisphere, the model reproduces the data well (r2 = 0.76, increasing to 0.87 if only 2007 and 2008 are considered). Outside of these periods, the model tends to have a negative bias with respect to the data (peaking at 34 ppb in 2005 and 2008). The model shows a larger drop off than the data when the chemical equator moves northward away from Darwin, perhaps indicating that the motion of the chemical equator is a more gradual process in time than described by the GEOS meteorological fields. It is also possible that there is a missing source, or a source that is underestimated in the model, outside of Australia. This would cause the model to underestimate the methane column when transport over Darwin is from that region. The difference between the data and the model shows a seasonal cycle, with minima during the summer months when the chemical equator lies to the north. During this time period, the prevailing winds at Darwin are from the north, while at other times of year the winds are predominantly from the south and east. Generally, the model reproduces the day-to-day variability in methane but not the overall trend. The modeled methane increases by about 5 ppb/year over the 3.5 year data record, while the data increases by about 8 ppb/year over the same time period.
 Figure 11 shows the model and measured surface CH4 at Darwin from a ground-based in situ FTS colocated with the TCCON instrument. The seasonal cycle in the residuals in both the surface data and the total column data is at a minimum during the Northern Hemisphere intrusions. Right after the intrusions, both increase. In the total column the residuals continue to increase throughout the dry season and decrease as the wet season begins again. At the surface, the residuals decrease through the year.
 Figures 10c and 11c show the monthly mean geographical tracers at Darwin, while Figure 8 shows the surface concentration tracers from the Australian regions broken down into sources. Intercontinental transport is stronger in the total column, reflecting that sources are emitted at the surface, whereas intercontinental transport into the region mainly occurs in the free troposphere. Emissions from the local region are the largest contributors to the concentrations above background at the surface. These are comprised of oceans, NEWWET, and biomass burning. The seasonal wetland source is largest in the wet season, when the wetlands are active, as expected. Emissions from biomass burning are larger in the dry season. Local emissions contribute 30–75% of the change to the surface concentrations above background and 10–50% of the added total column. Transport from Southeast Asia and the Southern Hemisphere tropics make comparable contributions to the total column in spring and summer, during the Australian-Indonesian monsoon. The relative contribution of the sources is similar from year to year, except in the case of seasonal wetlands, which are much stronger in 2006 and 2008.
 The behavior of the residuals between the model and measured concentrations at the surface and in the total column together with the tracers suggest reasons for the model-measurement discrepancy. In the first half of the year the residuals behave similarly, pointing to a common cause of the discrepancy. At this time of year, both surface and total column tagged tracers are dominated by local emissions from the West Tropical Australia region (mainly NEWWET) and transport from Southeast Asia and the SH Tropics. In the second half of the year, the residuals behave differently from one another. The total column tracers show greatest influence from transport from SE Asia and the SH Tropics, while the largest local source emitted in the region is biomass burning. The surface tracers are mostly biomass burning and ocean emissions from West and East Tropical Australia. The influence of transport from the Desert and Metropolitan regions for both the total column and surface concentrations is largest during the second part of the year. This suggests that at the surface, the emissions from the tropical regions of Australia are underestimated. The measurements of the total column are more affected by transport than measurements at the surface, which indicates an underestimated source lying north of Australia, or a source underestimated in the Desert or Metropolitan region.
7.3. Surface Concentrations Along the Ghan Train Route
 Figure 12 shows the hourly averaged ground-level methane concentrations measured by the in situ FTS installed on the Ghan train for the three campaigns held in 2008. Error bars on the measurements represent the standard deviation of the measurements over the hour. Local emissions contaminate the concentrations when the train stops in the cities of Alice Springs (23.7°S), Katherine (14.5°S), and Darwin (12.4°S), indicated by the vertical grey lines in Figure 12, and are not expected to be reproduced by the model.
Figure 12. Hourly averaged model and observed methane concentrations for the three Ghan train trips in (a–b) 26–29 February, (c–d) 30 March to 4 April, and (e) 28–30 September 2008, showing (left) northbound and (right) southbound trips. Error bars represent the standard deviation of the measurements. The GEOS-Chem model concentrations are shown with and without NEWWET. In Figures 12a–12e the difference between the data and the model is shown at the bottom. The vertical grey lines indicate the locations of Alice Springs (23.7°S), Katherine (14.5°S), and Darwin (12.4°S).
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 For all campaigns, the concentrations of methane gradually increase as the train moves northward into the tropics with a latitudinal gradient of 1.2 ± 0.2 ppb/degree latitude [Deutscher et al., 2010a]. The model latitudinal gradient of methane is 1.1 ± 0.3 ppb/degree latitude and 0.4 ± 0.2 ppb/degree latitude for the model with and without NEWWET, respectively. Without NEWWET, the model does not capture the increase in methane as the train moves northward toward the equator.
 Figure 13 shows results from the tagged tracer GEOS-Chem for the model run with NEWWET, which gives the source region for the change in methane concentration above background. The colored vertical lines indicate when the train moves from one region to another. The largest source in any given region is local sources from within that region, with influence from adjacent regions at the boundaries.
Figure 13. As Figure 12 but for tagged tracer concentrations. The vertical colored lines indicate the transition between the Metropolitan Australian region and the Desert region (blue) and between the Desert region and the West Tropical region (green).
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 Qualitatively, the model with NEWWET agrees with the data better than the model without, but some systematic lack of agreement remains. Some of the individual discrepancies could be due to the relatively coarse resolution of the model (2° × 2.5°). For all campaigns, NEWWET does not significantly affect the concentrations south of 20°S, as expected, where the model overestimates the concentrations by roughly 10 ppb for the first two campaigns and 0–20 ppb for the third.
 For the first campaign in February, the data and both of the model runs show an increase in methane concentration moving northward. In the model this is partly due to an intrusion from the Northern Hemisphere, as indicated by the influence from Southeast Asia in Figures 13a and 13b. North of 15°S the model with NEWWET and the data agree within error bars, while south of this the model overestimates the concentrations. For the northbound portion of this campaign, the model is 10–60ppb higher than the data in this region. Figure 13a shows that the overestimation of the concentration is due to emissions from the Western Tropical region of Australia, the majority of which is from seasonal wetlands. Owing to the gap in data between 16° and 18°S, where the model begins to see an increase in the methane concentrations, it is difficult to draw conclusions from this portion of the campaign. The mean difference between the data and the model for the entire campaign is −7.4 ± 10.8 ppb (−0.43%, RMS difference 11.7 ppb) without NEWWET, improving to −4.8 ± 7.0 ppb (−0.28%, RMS difference 10.1 ppb) with NEWWET.
 During the second campaign in March, the chemical equator was to the north of Darwin, and the entire train trip took place in the chemical Southern Hemisphere. This is confirmed by Figures 13c and 13d, which show very little influence from Southeast Asia but some influence from the Southern Hemisphere Tropics. Transport from other regions of Australia plays a larger role, indicating that the shift in surface winds associated with the end of the monsoon has occurred. The mean difference between the data and the model with NEWWET is −5.3 ± 11.3 ppb (−0.31%, RMS difference 12.3 ppb) and −10.0 ± 11.5 ppb (−0.58%, RMS difference 15.2 ppb) without them.
 For the northbound portion of the second campaign, the model displays a positive bias south of Alice Springs. North of this, the model and data agree within error bars until 20°S, where the data show a large increase in methane concentrations. This is roughly reproduced by the model with NEWWET, but is absent in the model without these emissions. Figure 13c indicates that this increase is caused by emissions from West Tropical Australia, which are dominated by emissions from the seasonal wetlands. In the southbound portion of the campaign, the peak in the data at roughly 20°S is caused by a local biomass burning event not included in the GFED emissions used in the model; as a result the model is not expected to reproduce this peak. North of this, the model without NEWWET agrees with the data within error bars, while the model with NEWWET remains about 10–15 ppb larger than the observations.
 For both of these campaigns, south of Alice Springs, the methane concentration is more constant, and the influence of the tagged tracers is small. Near Adelaide (34.9°S), emissions from Metropolitan Australia dominate. As the train moves further north into the Desert region, local emissions from this region and transport from South America are the largest contributors to the signal above background. The difference between the model and the data are most correlated to the local emissions from the Desert region (r2 ranging from 0.12 to 0.61). Emissions in this region are dominated by animals and termites. In the model, emissions from both sources are assumed to be constant throughout the year. Emissions from ruminant animals vary from year to year and are scaled to match the estimates from the Australian NGGI. Emissions from termites are known to vary with temperature and water availability, and possibly the model bias in this region could be a result of interseasonal variation in these sources that are not described by the model. The soil sink, which is treated as a constant in the model, could also vary with time. It is also possible that the soil sink is underestimated in the model, which could explain the positive bias in the model surface methane concentrations. In the same region there is little correlation between the model minus the measurements and the long-range transport tracers, suggesting the model describes the transport accurately. North of 20°S, the differences between the model and data are mainly due to NEWWET. This indicates that the seasonality and magnitude of the wetlands emissions is more complex than the seasonality of the gravity anomaly from GRACE, which we expect. Wetlands emissions vary not only with the water column and the temperature but also with other factors such available soil carbon and soil salinity.
 The third campaign took place during the dry season in September, and there are no emissions from seasonal wetlands during this time. Only the permanent wetland emissions are different between the two model runs, and as a result both runs are mostly similar. The model is roughly 20 ppb higher than the data south of 28°, but generally reproduces the gradient seen in the observations. The mean difference between the data and the model with NEWWET is −4.8 ± 7.8 ppb (0.27%, RMS difference 9.1 ppb) and −5.4 ± 7.6 ppb (0.31%, RMS difference 9.2 ppb) without them.
 Figure 13e indicates that the latitudinal gradient during this campaign is again a result of emissions from the West Tropical Australia region, here dominated by termites. As for the second campaign, there is very little influence from the northern hemisphere. Transport from South America is the second largest source when the train is in both the Desert region and the West Tropical region, consistent with the larger influence from these regions seen in the surface and column data. For this campaign, there is no strong correlation between the difference between the data and the model and any of the emissions or transport tracers, indicating that the overestimation is not dominated by any one source.