Assement of satellite - observed H RC data for rainfall estimates over the tropical Indian Ocean

Abstract

Satellite-observed HRC {Highly Reflective Cloud) data of 13 years from January 1971 to December 1983 are used for deducing open ocean rainfall over the tropical Indian Ocean. For this purpose, a comparison is made between satellite-observed monthly HRC frequency and monthly rainfall of eight island stations over the tropical Indian Ocean. Monthly frequencies of HRCs are statistically tested for linear regression relationship with 1248 stations months rainfall. Linear regression equation R=64.7+48.9 H (where R=Estimated rainfall and H= Monthly HRC frequency) and correlation coefficient (0.74) between HRC frequency and rainfall are found to be highly significant at 1% level. For the validation of the equation independent HRC data set for the year 1987 has been tested. Isohyetal patterns for this year obtained from HRC data are compared with Isohyetal patterns prepared by India Meteorological Department using.JNSAT-1B radiance data. Both the isohyetal patterns almost reflect the similar features. Mean isohyetal patterns derived from HRC data for the period 1971-1983 are found to be in. good agreement with the climatological synoptic events persisting over the tropical Indian Ocean. Therefore, It IS suggested that HRC data can be used with some confidence for rainfall estimates over the tropical Indian Ocean.