The physical mechanisms by which the leading patterns of SST variability impact U.S. precipitation

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Tuesday, 19 January 2010: 1:45 PM
B216 (GWCC)
Hailan Wang, NASA, Hampton, VA; and S. D. Schubert, M. J. Suarez, and R. D. Koster

This study uses the NASA NSIPP-1 AGCM to investigate the physical mechanisms by which the leading patterns of annual mean SST variability impact U.S. precipitation. The focus is on a cold Pacific pattern and a warm Atlantic pattern that exert significant drought conditions over the U.S. continent. Our investigation shows that while the cold Pacific and warm Atlantic are two spatially distinct SST patterns, they nevertheless produce similar diabatic heating anomalies over the Gulf of Mexico during warm season. The diabatic heating anomalies in both cases force an anomalous low-level cyclonic flow over the Gulf of Mexico that leads to reduced moisture transport into the central U.S. and increased moisture transport into the eastern U.S. The precipitation deficits over the Great Plains in both cases are greatly amplified by the strong soil moisture feedback in the NSIPP-1 AGCM. In contrast, the response over the SE U.S. to the cold Pacific during spring is primarily associated with an upper tropospheric high anomaly over the southern U.S. that is remotely forced by tropical Pacific diabatic heating anomalies, leading to greatly reduced stationary moisture flux convergences and anomalous subsidence in that region.