A computer model to study the variability of grid-based Sea Surface Temperature (SST) values derived from AQUA/AMSRE satellite data and its influence on the onset of South West Monsoon near the Kerala coastal region in India

A MATLAB-VBA program has been developed to generate contour maps of daily SST values over the whole globe pointing specifically to the Pacific Ocean region (covering -20deg to 10deg in latitude & 80deg to 240deg in longitude) affected by ENSO (El Nino & southern oscillation) events. Broad monthly time series of southern oscillation index (SOI) and that of total pixel (25 km times 25 km resolution) numbers having SSTs distributed between 27-31degC with 1degC interval are examined for different years of 2003-08 before the onset of SW monsoon. The pre-monsoon (Jan-Apr) averages showed that only in 4 out of 38 years of data, SOI exceeded 15 in the negative scale (strong El-Nino event) and for all of these years the monsoon onset dates were delayed. For all other values of SOI ranging between -14 to +15 no definite correlation exists. While there has been no occurrence of strong El Nino or La Nina events during 2003-08, the monsoon onset dates varied widely from 18 May to 8 June over Kerala coast. Results of this study show that the pattern of SST distribution during January-May of any year provides a better link to the likely onset dates. While larger number of pixels (Gt15,000-20,000) in the lower temperature band (27-28degC) produces normal monsoon onset, a smaller number (Lt10,000-15,000) gives rise to anomalous onset dates.