Annual and interannual variation of precipitation over the tropical Indian Ocean

The annual and interannual variability of precipitation over the tropical Indian Ocean is studied for the period June 1986 to December 1990 using the data retrieved from the Indian National Satellite (INSAT). The seasonal and annual rainfall over the Bay of Bengal was found to be about 2-3 times the Arabian Sea values. Harmonic analysis of the monthly mean rainfall showed that the annual wave has its largest amplitude in the northern Bay of Bengal, where the amplitude exceeds 250 mm/month, and the lowest amplitudes are found in the western Indian Ocean, especially off the Arabian and east African coasts. The INSAT and GOES Precipitation Index (GPI) rainfall estimates correlated reasonably well with the island rainfall data, with correlation coefficients of 0.83 and 0.78, respectively, whereas the special sensor microwave imager (SSMI) rainfall estimates had the lowest correlation (r = 0.64) with the island rainfall data. A comparison of the mean annual estimates by the three methods showed that the GPI rainfall estimates were higher than the INSAT and SSMI estimates by 16% and 41%, respectively, for the Indian Ocean area. The INSAT, GPI, and SSMI rainfall estimates document significant variations (both annual and seasonal) for arl the study areas, with the Indian Ocean area exhibiting maximum variability during the summer monsoon (June, July, and August) season.