Interannual displacements of convection and surface circulation over the equatorial Indian Ocean

Abstract

AbstractThe interannual variability of surface observations in the equatorial Indian Ocean is investigated from 23 years of ship reports (1954‐1976). In October and November, during certain years, the monthly analyses show strong wind anomalies in the eastern and central equatorial Indian Ocean. Simultaneously, cloud cover anomalies of opposite signs are observed in the eastern Indian Ocean and in the central Indian Ocean. A linear analysis of heat‐induced circulation suggests that the surface wind anomalies are forced by anomalies of rainfall. This circulation is probably dissipative with time scales in the range two to five days.The reasons for the maintenance of anomalous circulations are not well known. It is noted that during most El Niño events in the Pacific Ocean, anomalies are observed in the Indian Ocean. However, there are other years with the same anomalous pattern, 1961 for example. During the years with anomalously little cloudiness in the eastern Indian Ocean, sea surface temperatures lower than normal are found in the eastern Indian Ocean. This suggests that coupled air‐sea dynamics must be taken into account to understand the interannual variability.