Recent warming of tropical sea surface temperature and its relationship to the Northern Hemisphere circulation

Abstract

Analyses of the global sea surface temperature (SST) were performed to examine year to decade-scale variations of SST. It is found that the tropical SST, especially in the central and eastern Pacific and in the Indian Ocean, has being increasing since the late 1970’s. SST averaged in the whole tropics between 20ºN and 20ºS was warmer by about 0.3ºC~0.4ºC in the 1980’s than in the 1970’s. Convective activity in the tropics detected by the satellite-measured outgoing longwave radiation becomes more enhanced corresponding to the recent warming of the tropical SST. The Southern Oscillation Index, which represents a strength of the tropical Walker circulation, accordingly tends to become negative after the late 1970’s. The Pacific/North American teleconnection pattern with significant lowering of the geopotential height at 500 mb in the North Pacific has become dominant and persistent during winter seasons in the 1980’s. It is suggested that these large atmospheric anomalies may be associated with tropical heat sources enhanced by the recent warming of the tropical SST.