CLOUDS AND CLOUD RADIATIVE FORCING OVER TROPICAL INDIAN-OCEAN AND THEIR RELATIONSHIP WITH SEA-SURFACE TEMPERATURE

Earth radiation budget experiment (ERBE) radiative fluxes and Internat ional Satellite Cloud Climatology Project (ISCCP) C-2 cloud parameters for the four representative months of January, April, July and Octobe r and for the period 1985-1958 are used to study the cloud-radiation i nteraction over the tropical Indian Ocean (20 degrees S-20 degrees N, 50 degrees E-100 degrees E), and its relationship with sea surface tem perature (SST). Some important results are compared with those over tr opical west Pacific Ocean (20 degrees S-20 degrees N, 130 degrees E-18 0 degrees E), Over Indian Ocean, both the shortwave cloud radiative fo rcing (SWCRF) and longwave cloud radiative forcing (LWCRF) are found t o be correlated most with high cloud amounts (HCA) among the various c loud types. HCA and cloud radiative forcings in turn show a positive r elationship with SST above similar to 26.4 degrees C. During July and October, after reaching a maximum value at similar to 29 degrees C, th e relationship is found to be negative. In the rising portion of the H CA-SST relationship, at certain SST threshold value (27.4 degrees C fo r July) the probability of occurrence of high convective clouds sudden ly rises above 50%. During January and July above this SST threshold v alue the SWCRF is found to be significantly larger than LWCRF, thus ca using large negative net cloud radiative forcing. This is found to be associated with the sudden rise in the spatial extent (cloud amount) a nd the optical depth of the high clouds above the SST threshold values .