Tropical Coupled Air-Sea Feedbacks and Climate Variability

Ben Kirtman


The present study compares the local simultaneous correlation between rainfall/evaporation and sea surface temperature (SST)/SST tendency among observations, coupled general circulation model (CGCM; COLA and CFS) simulations, and stand-alone atmospheric general circulation model (AGCM) simulations. The purpose is to demonstrate to what extent the model simulations can reproduce the observed air-sea relationship. While the model simulated correlation agrees with the observations in tropical eastern Pacific, large discrepancies are found in the subtropics, mid-latitudes, and tropical Indo-western Pacific Ocean regions. In tropical Indo-western Pacific Ocean regions and the mid-latitudes where the atmosphere contributes to the observed SST changes, the specified SST simulations produce excessive SST forcing, whereas the CGCM captures the atmospheric feedback on the SST but with somewhat of an overestimation. In the subtropics, both the AGCM and CGCM produce unrealistic positive rainfall-SST correlation. In the tropical western-central Pacific and the North Indian Ocean, the CGCM simulated evaporation-SST correlation is opposite to the observed due to an excessive dependence of the sea-air humidity difference on the SST. Additional numerical experiments demonstrate the importance of maintaining coupled air-sea feedbacks in the Indian Ocean in order to reproduce observed atmosphere-ocean co-variability.