The heat balance of the Indian Ocean

The tropical Indian Ocean exhibits a dynamical and thermodynamical structure that is very different to the other tropical ocean basins. In response to the substantial seasonal reversals of the annual monsoon winds, the Indian Ocean undergoes extreme transitions of its dominant currents as well as a strong cycle in sea-surface temperature (SST) in the tropical regions. During the boreal spring the northern Indian Ocean SSTs are some of the warmest on the planet. The coupled air-sea interaction between the ocean and atmosphere conspire to produce the strong intraseasonal and interannual variability in circulations and rainfall of the South Asian summer monsoon.; The ability of the ocean dynamics to regulate SST is examined. In comparing the Pacific to the Indian Ocean, it is noted that for the two regions, both surface heat flux and prevailing atmospheric conditions are vastly different. Processes which exist in the Pacific “warm pool” region to limit increases in SST are strongly constrained in the Indian Ocean. It is argued that SST regulation in the Pacific Ocean is a combination of local thermodynamical balance and changes in the large-scale atmospheric circulation. In the Indian Ocean, SST is regulated by strong advection of heat southward across the equator and by changes in heat storage. The importance of different processes in different regions of the tropical warm pool is discussed, and it is argued that the upper ocean seeks a dynamic equilibrium in the most expeditious manner available in the particular location.; Satellite and numerical model reanalysis data are used to show that the atmosphere over the North Indian Ocean undergoes strong interannual variability which appears to be related to both the strength of the South Asian monsoon and the El Niño-Southern Oscillation (ENSO). The behavior of the North Indian Ocean is examined using an intermediate ocean model. It is shown that there is substantial variability in ocean dynamical and thermodynamical structures, commensurate with the atmospheric forcing.; The dynamics of the Indian Ocean heat balance are investigated closely. The roles of the wind-driven circulation and the oceanic mixed layer and their interannual variability is analyzed in terms of its effect on meridional heat transport and heat storage. It is found that the dominant component of heat transport north of 12°S is the wind-driven Ekman transport, with the pressure gradient driven transport providing a secondary mechanism. The variation of the strength of these components on interannual timescales is examined.