Previous studies by us and others have suggested that both the Pacific and Atlantic Oceans have influenced persistent droughts in North America. Therefore, the combined effects and interactions of both oceans must be understood and evaluated in order to determine the predictability of their effects on persistent drought variations in the North America. Given the controversial medieval SST anomalies in the tropical Pacific and the persistent basin-wide warm SST anomalies in North Atlantic, we hypothesize that during medieval times (MT, approximately 900-1300AD), the Atlantic Ocean played a more important role relative to the Pacific Ocean on the droughts in North America than it does at present. To examine this hypothesis we have the following two objectives:

1. Examine the relative role of Pacific and Atlantic SST anomalies in the medieval droughts in North America; and
2. Decipher the physical mechanisms by which SST anomalies may have induced the medieval droughts.

Because the model forced by SST anomalies in the Pacific and Atlantic Oceans cannot simulate the wind direction changes in the central U.S. during MT (Feng 2008), we further hypothesize that the change in land surface-atmosphere interactions due to devegetation and reduction in soil moisture led to the change in summertime winds from southeasterly to southwesterly. To examine this hypothesis we have the following objective:

3. Determine the role of land surface processes and feedbacks on medieval drought. Particularly, identify the effect of devegetation and soil moisture on the drought, and their role in changes of the surface wind direction in the Great Plains.