Soil moisture impacts on convective indices and precipitation over complex terrain

Abstract

The impact of soil moisture on convective precipitation, convective indices, surface energy balance components, and near-surface meteorological variables is analysed for seven intensive observation periods of the Convective and Orographically induced Precipitation Study (COPS) conducted in summer 2007 using a non-hydrostatic limited-area atmospheric prediction model. The control runs are compared to sensitivity experiments under dry (-25 %) and wet (+25 %) initial soil moisture conditions. In the wet experiment, surface fluxes produce moister and cooler boundary layers with increased equivalent potential temperatures. Furthermore, the lifting condensation level and the level of free convection are lowered for all analysed regions, even under different synoptic controls. The comparison of boundary-layer and mid-tropospheric forcing regimes reveal that the impact of soil moisture on the atmosphere is not systematically higher for boundary-layer forcing. Whereas the Bowen ratio exhibits a clear dependence on soil moisture conditions, the impact on precipitation is complex and strongly depends on convective inhibition. A considerable, but non-systematic dependence of convective precipitation on soil moisture exists in the analysed complex orography. The results demonstrate the high sensitivity of numerical weather prediction to initial soil moisture fields.