Signals of interannual and interdecadal variability of air‐sea interaction in the basin‐wide Indian Ocean

Abstract

Many climatolo gists are concerned with the variability of air‐sea interactions. In this paper, signals of interannual and interdecadal variability of air‐sea interactions in the southern subtropical Indian Ocean (SSIO) have been extracted from both monthly sea surface temperatures (SST) and monthly surface winds and compared to air‐sea interactions of the tropical Indian Ocean (TIO). Empirical orthogonal function (EOF) expansion has been used in the analysis of observed sea surface temperature anomalies (SSTA) over the basin‐wide Indian Ocean (35°S to 15°N, 30°E to120°E)for 1950–1998. The results show that another dipole structure, with centres in the south‐western subtropics of the ocean and near Australia, is different from the TIO dipole mode in several aspects. The SSIO dipole mode reflects internal variations of the Indian Ocean, exhibiting obvious interannual and interdecadal changes. The variability of this independent SSTA mode, which is represented by a dipole mode index (DMI), is strongly connected with the air‐sea coupling through monsoon precipitation, wind field, and heat flux changes. Examining the wind fields correlated with the SSIO SSTA DMI, an oscillation in the meridional surface wind or the wind DMI is also defined and analyzed. Composite results of wind fields from extreme years and anomalous periods of the SSIO SSTA DMI show that interannual and interdecadal air‐sea interactions are evident in the Indian Ocean and are connected with the activity of the east Asian, the south Asian, the African, and the Australian monsoons.