Seasonal Changes in Tropical SST and the Surface Energy Budget under Global Warming Projected by CMIP5 Models

Abstract

he seasonal changes in tropical SST under global warming are investigated based on the representative concentration pathway 8.5 (RCP8.5) and historical runs in 31 models from phase 5 of CMIP (CMIP5). The tropical SST changes show three pronounced seasonal patterns: the peak locking to the equator throughout the year and the weaker equatorial changes and stronger hemispheric asymmetric changes (HACs) in boreal autumn. The magnitude of the seasonal patterns is comparable to the tropical-mean warming and the annual-mean patterns, implying great impacts on global climate changes. The peak locking to the equator is a result of the equatorial locking of the minimum damping of climatological latent heat flux and the ocean heat transport changes. Excluding the role of ocean heat transport suggested in previous studies, the weaker equatorial warming in boreal autumn is contributed by stronger evaporation damping as a result of stronger climatological evaporation and increased surface wind speed. The seasonal variations of the HAC are driven by the variations of the damping effect of climatological evaporation. In boreal summer, the damping effect of climatological evaporation, which is greater in the Southern Hemisphere, promotes the development of the HAC. Consequently, the HAC peaks in boreal autumn when the damping effect of climatological evaporation transforms to a reverse meridional pattern, which is greater in the Northern Hemisphere. The wind?evaporation?SST feedback, as the key process of the annual-mean HAC, amplifies the seasonal variations of the HAC in tropical SST.