ANNUAL AND INTERANNUAL VARIATION OF PRECIPITATION OVER THE TROPICAL INDIAN-OCEAN

The annual and interannual variability of precipitation over the tropi cal Indian Ocean is studied for the period June 1986 to December 1990 using the data retrieved from the Indian National Satellite (INSAT). T he 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 mont hly mean rainfall showed that the annual wave has its largest amplitud e in the northern Bay of Bengal, where the amplitude exceeds 250 mm/mo nth, 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 we ll with the island rainfall data, with correlation coefficients of 0.8 3 and 0.78, respectively, whereas the special sensor microwave imager (SSMI) rainfall estimates had the lowest correlation (r = 0.64) with t he island rainfall data. A comparison of the mean annual estimates by the three methods showed that the GPI rainfall estimates were higher t han the INSAT and SSMI estimates by 16% and 41%, respectively, for the Indian Ocean area. The INSAT, GPI, and SSMI rainfall estimates docume nt significant variations (both annual and seasonal) for arl the study areas, with the Indian Ocean area exhibiting maximum variability duri ng the summer monsoon (June, July, and August) season.