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

Abstract

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 −20° to 10° in latitude & 80° to 240° 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 × 25 km resolution) numbers having SSTs distributed between 27-31°C with 1°C 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 (≫15,000–20,000) in the lower temperature band (27–28°C) produces normal monsoon onset, a smaller number (≪10,000–15,000) gives rise to anomalous onset dates.