Why is the Bay of Bengal experiencing a reduced rate of sea surface warming?

摘要

The sea surface temperature (SST) in the Bay of Bengal (BoB) during the period 1960-1995 showed a decadal cycle, riding over a warming trend. The disruption of the decadal cycle was noticed post-1995 and was followed by a slowdown in the sea surface warming. The cause for the disruption of the SST decadal cycle was the weakening of the link between SST and sunspot number. The rising trend in the SST is due to the increasing atmospheric CO2 concentration. The post-1995 SST slowdown was due to the increasing influence of the number of depressions, cyclones and severe cyclones in the BoB, the occurrence of which showed an upward trend. Using Price-Weller-Pinkel model we show that cyclonic systems deepen the mixed-layer through enhanced mechanical-mixing with cooler sub-surface waters, thereby reducing the mixed-layer temperature and consequently the SST. This process opposes the SST rise due to increasing atmospheric CO2 concentration. The net effect of the wind-mixing caused by the increased number of depressions, cyclones and severe cyclones and the increased CO2 concentration is a SST slowdown in the BoB. This mechanism differs from the SST slowdown mechanisms suggested for the Atlantic and the Pacific.