Exploring the tropical Response to Global Warming via an Overriding Technique

Abstract:

A suite of partial coupling experiments have been devised under a coupled GCM framework to isolate the effects of the feedbacks from the change of the wind-driven ocean circulation and air–sea heat flux in the global climate response to the forcing of increasing CO₂. Specifically, the SST response has been examined in the tropical Indo-Pacific. An El Nino-like SST warming emerges in the tropical Pacific, together with an overall shoaling of the equatorial thermocline. The wind stress change plays the leading role in weakening the surface westward currents as well as for the oceanic changes in the equatorial thermocline while the effect of the wind speed change is mainly confined to the surface. In the tropical Indian Ocean (TIO), an Indian Ocean Dipole (IOD) like warming pattern is generated, and the development of the dipole pattern shows a pronounced seasonal evolution. Results from overriding experiments show that the wind-evaporation-sea surface temperature (WES) feedback accounts for most of the enhanced warming in the western and central TIO during May–July with the reduced southerly monsoonal wind and partially contributes to the reduced warming in the eastern TIO during June-September. The Bjerknes feedback explains most of the reduced warming in the eastern TIO during August-October, accompanied by reduced precipitation in the eastern TIO, easterly wind anomalies and a thermocline shoaling along the equator. Both feedbacks facilitate the formation of the dipole warming pattern in the TIO.