The sensitivity of the global atmospheric response to tropical SST anomalies throughout the year has been systematically investigated using the NCAR CCM3 AGCM. Model responses were first determined for an array of 43 localized SST anomaly patches over the Indian, Pacific, and Atlantic oceans. Ensembles of 16 or more integrations were made for each patch, with both positive and negative SST anomalies. Results from the forcing experiments were then combined using a novel smoothing procedure to produce sensitivity maps for target quantities of interest.

The focus in this talk will be on the sensitivities of North American precipitation and temperature to tropical SST forcing throughout the year. Results will be compared with those from the less ambitious study of Barsugli and Sardeshmukh (JCL 2002), that investigated only wintertime sensitivities, only to Indo-Pacific SSTs, and in another AGCM (the NCEP MRF9). The agreement is good enough to increase confidence in the results from both studies. It is again demonstrated that North American precipitation and temperature are equally if not more sensitive to SST anomalies outside the areas of strongest ENSO-related tropical SST variability. This not only implies that one should go "beyond ENSO" to maximize interannual climate predictability over North America, but also provides insight into how longer-term changes in the North American climate may be sensitive to non-ENSO-like tropical SST changes (e.g., the recent trend in Indian ocean SSTs). The substantially different sensitivities demonstrated here of both precipitation and temperature in winter and summer also affect the sensitivity of prolonged North American drought (which is an integrated measure of the two variables) to tropical --- and especially to the "non ENSO" --- SSTs.