Changes in the sensitivity of tropical rainfall response to local sea surface temperature anomalies under global warming

摘要

Changes in tropical rainfall variability under global warming are crucial to rainfall changes induced by tropical sea surface temperature (SST) variability modes, which exerts severe influences on human society and the natural environment. As the main factor influencing tropical rainfall variability, changes in the sensitivity of tropical rainfall response to local SST anomalies under global warming remain unclear. This study reveals its two dominant spatial features based on the multi-model ensemble mean result from phase 5 of the Coupled Model Intercomparison Project. The sensitivity of tropical rainfall response to SST anomalies is enhanced in the equatorial central-eastern Pacific, and exhibits a positive Indian Ocean dipole-like pattern in the Indian Ocean. A simplified moisture budget decomposition shows that such change is composed of the thermodynamic effect induced by the increase in mean-state moisture and the dynamic effect induced by the changes in the sensitivity of atmospheric circulation response to SST anomalies. When the thermodynamic effect, displaying a 'wet-get-wetter' paradigm, is basically offset with a part of the dynamic effect by the general weakening of atmospheric circulation response to SST anomalies under global warming, changes in the sensitivity of rainfall response to SST anomalies is dominated by a residual dynamic effect that reflects the roles of two factors: the spatially non-uniform SST warming and the climatological SST. As a result, the 'warmer-get-wetter' paradigm is more important to changes in the sensitivity of rainfall rasponse to SST anomalies than to climatological rainfall changes. Moreover, the non-uniform SST warming pattern and the climatological SST are also important sources of intermodel uncertainty in the changes of sensitivity of rainfall rasponse to SST anomalies.