A feedback mechanism between soil‐moisture distribution and storm tracks

Abstract How the distribution of soil moisture impacts the location and persistence of the storm track and the resulting distribution of precipitation is investigated. Particular attention is given to North America where an extensive series of numerical experiments using a regional climate model are performed to investigate these issues. The findings suggest that soil‐moisture distribution has a pronounced impact on the large‐scale dynamics via a meridional displacement of the storm track. The displacement tends to enhance the local soil moisture–rainfall feedback over the region of the anomaly. The initial feedback is induced by the local effects of soil moisture on the boundary‐layer energy budget and then propagated to the large‐scale through modifications to the geopotential heights. Because of soil moisture's impact on the large‐scale dynamics, a local soil‐moisture anomaly can induce both flood‐ and drought‐like conditions in surrounding regions. Experiments with a dry anomaly applied either over the upper Midwest or Great Plains display a northward shift in the storm track. This shift tends to result in drought‐like conditions in the region of the anomaly and both flood‐ and drought‐like conditions in surrounding regions. Anomalous wetting in the Southwest impacts the distribution of precipitation not only locally, but also over most of the United States; drought‐like conditions are simulated to the north and east of the anomaly region while flood‐like conditions are simulated locally and eastward. Overall, the impacts of soil‐moisture distribution on the large‐scale dynamics and the location and intensity of the storm track play a significant role in determining summer rainfall distribution. Soil‐moisture anomalies over relatively small regions can induce floods and droughts not only locally, but also over remote regions. Copyright © 2003 Royal Meteorological Society.