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Friday, January 27, 2012

Why is Indian Ocean warming consistently? by Suryachandra A. Rao et al., Climatic Change 110 (2012); doi: 10.1007/s10584-011-0121-x

Climatic Change, 110(3-4) (2012) 709-719; doi: 10.1007/s10584-011-0121-x

Why is Indian Ocean warming consistently?


Observations have shown that the Indian Ocean is consistently warming and its warm pool is expanding, particularly in the recent decades. This paper attempts to investigate the reason behind these observations. Under global warming scenario, it is expected that the greenhouse gas induced changes in air–sea fluxes will enhance the warming. Surprisingly, it is found that the net surface heat fluxes over Indian Ocean warm pool (IOWP) region alone cannot explain the consistent warming. The warm pool area anomaly of IOWP is strongly correlated with the sea surface height anomaly, suggesting an important role played by the ocean advection processes in warming and expansion of IOWP. The structure of lead/lag correlations further suggests that oceanic Rossby waves might be involved in the warming. Using heat budget analysis of several ocean data assimilation products, it is shown that the net surface heat flux (advection) alone tends to cool (warm) the ocean. Based on above observations, we propose an ocean-atmosphere coupled positive feedback mechanism for explaining the consistent warming and expansion of IOWP. Warming over IOWP induces an enhancement of convection in central equatorial Indian ocean, which causes anomalous easterlies along the equator. Anomalous easterlies in turn excite frequent Indian ocean dipole events and cause anti-cyclonic wind stress curl in south-east and north-east equatorial Indian ocean. The anomalous wind stress curl triggers anomalous downwelling oceanic Rossby waves, thereby deepening the thermocline and resulting in advection of warm waters towards western Indian Ocean. This acts as a positive feedback and results in more warming and westward expansion of IOWP.

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