Seasonal Delay of Tropical Rainfall Enhanced by the Interhemispheric Contrast of SST Warming

Abstract

The seasonal delay of tropical rainfall is a robust feature under global warming. This study finds that the seasonal delay of tropical rainfall is much more pronounced under spatially patterned sea surface temperature (SST) warming compared to uniform SST warming. Through the lens of the atmospheric energetic framework, we show that the enhanced seasonal delay is primarily driven by the interhemispheric contrast in SST warming between the Northern and Southern Hemispheres, which intensifies the inter-seasonal difference in cross-equatorial atmospheric energy transport between transition seasons. The SST warming features are found to be crucial, characterized by both its seasonal cycle and annual mean. The former is closely related to the seasonal delay of SST, especially in the northern high latitude, while the latter is further demonstrated by an atmospheric model forced with the annual-mean spatially patterned SST warming.