Interannual variability of the sea-surface temperature in the Indian Ocean in response to the air–sea turbulent heat exchange

Abstract

Abstract We investigate the interannual variability of the sea-surface temperature (SST) regulated by the thermal and dynamical forcings at the sea surface associated with seasonal changes of the monsoon circulation in the Indian Ocean. Analysis is done with satellite observations from July 1987 to December 1998. Interannual variations of the air–sea thermal exchange are examined along a path that defines the main monsoon circulation. Taking into account the advection by meridional atmospheric circulation, we show that the anomalous moisture contents are transferred meridionally from south of the equator to the north during the southwest monsoon. It is also shown that the interannual signals from north and south of the equator can be reduced in the equatorial region as a result of convergence of the wind during the northeast monsoon. Due to the synchronous changes of wind and SST anomalies, which have opposite effects on the turbulent heat flux, the air–sea thermal coupling is minimized in the western tropical Indian Ocean on an interannual time scale. In the equatorial region, the resultant air–sea thermal exchange at low latitude almost depends on the atmospheric condition in the mid latitude instead of the thermal condition at the sea surface. In addition, it is thought that the interannual variation of the SST at the equatorial zone is mainly controlled by the wind-induced heat transport in the western and the central areas. In contrast, the SST anomalies in the eastern half of the basin are usually controlled by the surface thermal forcing except for the marked ENSO years. It is suggested that the east–west contrast of heating anomalies due to the wind driven heat transport may affect the oceanic heat balance in the eastern tropical Indian Ocean. The SST anomaly in the southern mid latitude is thermally controlled by the air–sea heat exchange. Our results suggest that the SST anomalies in the mid and low latitudes are linked and modulated through the meridional transport of atmospheric anomalies, although they are determined by the distinct processes.