Model study of soil-moisture influence on precipitation seesaw in the southern United States

A coupled atmosphere–land-surface mesoscale model is used to assess the responses of precipitation to soil-moisture anomalies in two regions: (1) the core region of the North American Monsoon (NAM; 105°—112°W, 24°—36°N); (2) the central–southern United States (CS-US; 85°—95°W, 30°—36°N). Results from a series of numerical experiments integrated from July to September 2000 show that precipitation increases in the NAM region in July with a prescribed wet soil-moisture anomaly; meanwhile, precipitation decreases in the CS-US region. In the following months, when the prescribed wet soil-moisture anomaly in the NAM region was removed, the increase in precipitation in the NAM region becomes weaker and shifts eastward to the CS-US region. By September, an inverse precipitation seesaw in these two regions is built up. Except for local evaporation, the transportation of atmospheric moisture affects the interaction between soil moisture and precipitation, especially in the regions and periods without the prescribed soil-moisture anomaly. The soil-moisture anomaly in the NAM region is only partially responsible for the precipitation seesaw in the southern United States.