The impact of sea surface temperature on the North American monsoon: A GCM study

Abstract

The NCAR CCM3 was used to simulate the circulation and rainfall patterns of the North American monsoon system (NAMS). When forced with repeated annual cycles of climatological average sea surface temperatures (SSTs), the CCM3 significantly under‐represents monsoon rainfall in the southwest United States while simulating excessive precipitation in the tropical eastern Pacific Ocean and the Caribbean Sea. However, when forced with the observed monthly average SSTs from 1979 to 1997, the CCM3 produces an improved simulation of monsoon rainfall in the southwestern U.S., as well as in the eastern tropical Pacific Ocean and the Caribbean Sea. Using the SSTs for 1983 in the Pacific and climatological SSTs elsewhere, the modeled circulation and rainfall distribution resembles that given with observed monthly average SSTs. The simulations are sensitive to the size of the domains over which the Pacific SST anomalies are imposed. Overall, these results suggest that the magnitude and size of winter‐ and springtime Pacific SST anomalies have a significant influence on summertime rainfall in the southwest U.S., and that these SSTs contribute to the NAMS precipitation climatology in extreme years more than in less extreme years.