Combined Effect without Soil Moisture Feedback Mechanistic Studies with NASA Model Helps Us Understand the Impacts of Pacific and Atlantic Oceans on U.S. Precipitation Warm Atlantic Cool Pacific Combined Effect Major drought Summer Precipitation Anomalies (mm/day) A cool tropical Pacific and warm tropical Atlantic combine to produce drought in the Great Plains. These are similar to the ocean conditions that occurred during the 1930s Dust Bowl Drought. When the anomalies in each ocean are the same sign, the effects cancel each other. Disabling soil moisture feedback greatly reduces the severity of the drought. Combined Effect without Soil Moisture Feedback Top panels show the impact on JJA precipitation of forcing the NSIPP-1 AGCM with cold Pacific and warm Atlantic SST anomalies. The SST anomalies consist of +/-2 standard deviations of the leading EOFs of the annual mean SSTs based on the period 1901-2004. We found that cold (warm) Pacific SST anomalies tended to produce drought (pluvial) conditions in the Great Plains, while cold (warm) Atlantic SST anomalies tended to produce pluvial (drought) conditions in the Great Plains. In the case when they are opposite signed in the two basins they tend to reinforce the impact on the Great Plains (cold Pacific and Warm Atlantic produced major drought, while warm Pacific and cold Atlantic produced very pluvial conditions), while if they are like-signed anomalies they tend to cancel the impacts on the Great Plains. In either case, inhibiting land-atmosphere interactions tends to reduce the impacts of the SST anomalies in the Great Plains (lower right panel). A cold Pacific and warm Atlantic are ocean conditions similar to that that occurred during the 1930s Dust Bowl Drought. The bottom left shows a Dust storm approaching Stratford, Texas. Dust bowl surveying in Texas April 18, 1935. NOAA George E. Marsh Album 1930s Dust Bowl Drought: Cool Pacific, Warm Atlantic Reduced drought