The Response of Precipitation to Initial Soil Moisture over the Tibetan Plateau: Respective Effects of Boundary Layer Vertical Heat and Vapor Diffusions

This study investigates the influences of initial soil moisture over the Tibetan Plateau (TP) on precipitation simulation, and the respective effects of boundary layer vertical diffusion for heat (Kh) and vapor (Kq). Results indicate that the responses of boundary layer vertical diffusion to soil moisture are obvious mainly in the daytime. Wetter land surface corresponds to weaker vertical diffusion, which could strengthen thermal forcing and dynamic lifting in the lower atmosphere, and encourage water vapor saturation near the top of boundary layer to prevent the environmental dry air entrainment/invasion, which would be beneficial to more convection and precipitation. Wetter land surface over the TP could enhance the contrast between the cold in the northwestern TP and the warm in the southeastern TP, which would be conducive to the southeastward propagation of precipitation. The simulation of heat and moisture in the boundary layer could be improved by perturbing the relative intensity of Kh and Kq. From the perspective of heat and moisture, Kh affects atmospheric stability, while Kq affects moisture and its vertical transport in the boundary layer. The Kh and Kq have competitive effects on precipitation intensity by influencing the relative importance of moisture and atmospheric stability conditions in the boundary layer. Adjusting the relative intensity of Kh and Kq would deactivate the competitive effects. Stronger Kh but weaker Kq would alleviate the overestimated precipitation by inhibiting vertical transport of moisture to the top of boundary layer and attenuating convective instability in the boundary layer. SIGNIFICANCE STATEMENT: The purpose of this study is to better understand the effects of boundary layer vertical heat and moisture diffusion in the response of precipitation to soil moisture. This is important because boundary layer vertical diffusion is a crucial factor influencing the relation between soil moisture and precipitation. Our results reveal the competitive effects of boundary layer vertical diffusion for heat and vapor on the simulation of precipitation. These results point a potential way toward better understanding the response of precipitation to soil moisture.