Investigating the Mechanisms of Shallow Precipitating Clouds Formation during the HI-SCALE Field Campaign

Description

Shallow precipitating clouds are often a precursor to subsequent deep convection. This study investigates the land-atmosphere interactions and boundary layer processes that lead to the formation of such clouds over the Southern Great Plain during Holistic Interactions of Shallow Clouds, Aerosols and Land-Ecosystems (HI-SCALE) field campaign in 2016. High-resolution simulations of a selected case of transition from clear-sky to shallow precipitating clouds and then to the deep convection transition are conducted using a Large Eddy Simulations (LES) version of the Weather Research and Forecasting (WRF) Model. We perform the LES version of WRF simulations with the modified initial and boundary conditions to isolate the locally driven convections from the transport of the convections outside the domain. The comparative impacts of advection and surface forcing on the diurnal cycle of the shallow clouds are examined. Besides, the vertical mass transports are analyzed by isentropic analysis to study the impacts of land surface properties (i.e. land use type, surface fluxes, soil moisture, etc.) on the initializations of the shallow clouds and the precipitation of these clouds. We found that (1) convection points start with high equivalent potential temperature (θ_e). As rain is formed, rain falls over the low θ_e environment; (2) convection prefers to occur over grassland and forest, rather cropland, urban and water; (3) convection also prefers to occur over the regions with high latent heat flux, low sensible heat flux, and high soil moisture. We also examine the detailed mechanisms related to the above processes by cluster analysis.