Simulated seasonal and interannual variability of mixed layer heat budget in the northern Indian Ocean
DeBoyer Montegut, C.
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A global Ocean General Circulation Model (OGCM) is used to investigate the mixed layer heat budget of the Northern Indian Ocean (NIO). The model is validated against observations and shows a fairly good agreement with mixed layer depth data in the NIO. The NIO has been separated into three sub-basins: the western Arabian Sea (AS), the eastern AS, and the Bay of Bengal (BoB). This study reveals strong differences between the western and eastern AS heat budget, while the latter basin has similarities with the BoB. Interesting new results on seasonal time scales are shown. Penetration of solar heat flux need to be taken into account for two reasons. First an average of 28.6Wm-2 is lost beneath the mixed layer over the year. Second, the penetration of solar heat flux tends to reduce the effect of solar heat flux on the SST seasonal cycle in the AS because seasons of strongest flux are also seasons of thin mixed layer. This enhances the control of SST seasonal variability by latent heat flux. Impact of salinity on SST variability is demonstrated. Salinity stratification plays a clear role in maintaining a high winter SST in the BoB and eastern AS while not in the western AS. The presence of fresh water near the surface allows to store heat below the surface that can later be recovered by entrainment warming during winter cooling (with a winter contribution of +2.1 degC in the BoB). On interannual timescale, the eastern AS and BoB are strongly controlled by the winds through the latent heat flux anomalies. In the western AS, vertical processes and also horizontal advection contribute significantly to SST interannual variability and the wind is not the only factor controlling the heat flux forcing.
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