Predictability of Tropical Pacific Decadal Variability and North American Drought.

The PIs will explore the predictability of the tropical Pacific climate and its impact on precipitation over North America. 1) They will use a hierarchy of models and statistical techniques to assess hindcast skill and potential predictability of observed decadal variations in tropical Pacific SSTs throughout the post 1856 period of instrument observations. 2) They will use atmosphere GCMs forced by observed SSTs in different regions of the tropics to determine what it is in the tropical SST patterns that forces persistent droughts in mid-latitudes, including North America. 3) They will compare with experiments that use different repeating seasonal cycles (e.g., one averaged over the 1930s) to determine what extent decadal precipitation anomalies can be simulated if only the shifts in the mean state of the tropical Pacific is known. 4) If the skill in the SST forecasts warrants it, they will perform hindcasts of decadal precipitation anomalies over North America using a two-tiered approach in which hindcasts of teh tropical Pacific SSTs will be used to force the atmospheric GCM. The modeled precipitation anomalies will be verified against station data or tree ring reconstructions.