Understanding model dependence of the impact of leading SST variability over the U.S.: a US CLIVAR drought working group effort [INVITED]

The recent model simulations initiated by the U.S. Climate Variability and Predictability Research Program (USCLIVAR) drought working group provide an excellent opportunity to address the issue of the model dependence in representing the linkages between the leading SST patterns and U.S. drought and to investigate the mechanisms through which the leading SST patterns affect the regional hydroclimate in the current generation of AGCMs. The leading patterns of SST variability consist of a Pacific ENSO-like pattern, an Atlantic pattern that resembles the Atlantic multidecadal oscillation, and a global linear trend pattern. The runs were done with several global atmospheric models including the NASA/NSIPP-1, NCEP/GFS, GFDL/AM2, and NCAR CCM3 and CAM3.5. In this talk, we first present an overview of the model intercomparison of the responses over the U.S. to the leading SST patterns. We then focus on the USCLIVAR simulations produced by the NASA NSIPP-1 AGCM, and discuss the physical and dynamical mechanisms through which the SST patterns affect the U.S. climate. In particular, we address the reasons for the similarity in the warm season precipitation responses over the Great Plains to the cold Pacific and warm Atlantic, and the causes for the distinct seasonality in the Southeast (SE) U.S. precipitation response to the cold Pacific. Finally, our findings on the mechanisms are used to understand the model dependence of the responses over the U.S. to the leading SST patterns.