The Indian Climate Research Programme (ICRP) has formulated the Continental Tropical Convergence Zone (CTCZ) programme to understand the mechanisms leading to space-time variation of the CTCZ and the embedded monsoon disturbances during the summer monsoon. The complete overview and detailed objectives of CTCZ programme is available at http://www.imd.gov.in/SciencePlanofFDPs/CTCZ. Under this national program (CTCZ), oceanic and atmospheric observations are taken on-board ocean research vessel (ORV) Sagar Kanya (SK-261). The cruise track is shown in Figure 1. The research vessel started on 15th July 2009 from the port of Chennai and reached the time series location (TSL) at 89° E, 19° N on 22nd July and stationed there for 15 days (up to 6th August). Two hourly profiling up to the depth of 760 m was done for the measurement of salinity and temperature. Total 218 profiles were measured using Conductivity-Temperature-Depth (CTD) instrument, manufactured by Idronaut. To estimate the horizontal advection of salinity and temperature, CTD measurement at 4 other locations situated at North, South, East and West of the TSL and at a distance of 3 nautical miles from the TSL were carried out. In order to avoid the influence of solar insolation, the CTD measurement at North, South, East and West locations are done once at night and up to the depth of 150 m. The temperature and conductivity sensor of Idronaut CTD has an accuracy of 0.001° C and 0.0001 Sms−1 respectively and scan frequency is of 40 Hz. The speed of probe during downcast and up-cast was between 0.5–1 m s−1. The downcast and up-cast data were averaged into 1m depth bins. The tendency of temperature and salinity can be calculated by using the following equations [Nisha et al., 2009]:
where, T is the ocean water temperature, u, v, w are zonal, meridional and vertical component of the currents, Qnet is the net surface heat flux, ρ is the density of water, h is the mixed layer depth, CP = 3993.0J kg−1K−1 is the heat capacity of water, D represents tendency due to diffusion, S is the salinity of water, E, P are evaporation and precipitation rate respectively. wh is the vertical advection below mixed layer (m month−1), H is the Heaviside step function [=0 if (wh + ) > 0, = 1 if (wh + ) < 0] and Sh is the salinity just below the mixed layer base.
 The net surface heat flux is used from NCEP reanalysis [Kalnay et al., 1996]. The oceanic u, v currents are from NCEP Global Ocean Data Assimilation System (GODAS, data provided by the NOAA/OAR/ESRL PSD, Boulder, Colorado, USA, from their Web site at http://www.esrl.noaa.gov/psd/). High resolution oceanic currents (Ekman and geostrophy) are derived using quick scatterometer (QuikSCAT) [Ebuchi et al., 2002] wind and AVISO (Analysis, Validation and Investigation of Satellite Oceanography) sea surface height data [Ducet et al., 2000] respectively. The Ekman current is calculated using the following equation:
where Coriolis force f = 2Ω sin θ, ρo = mixed layer ocean water density. wind stress τx = ρaCDu2 and τy = ρaCDv2, with CD = 1.5 × 10−3, ρa = 1.252 kg m−3. Using sea surface height (H) data, the geostrophic current is calculated using the following equation:
In addition to the cruise data, we have used daily surface layer salinity, temperature and rainfall measured at 15° N, 90° E from RAMA Buoy for the period October 2008 to December 2010 [McPhaden et al., 2009]. Daily rainfall data from GPCP are used in order to identify the large scale monsoon events (http://precip.gsfc.nasa.gov/index.html). In addition to that, high resolution daily rainfall data from 3B42 [Huffman et al., 1995, 2007] for the period 1st June to 31st December 2009 are used.