Impacts of Land-atmosphere Interactions on Convection Initiations over Southern Great Plains

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 observed over the Southern Great Plain during the Holistic Interactions of Shallow Clouds, Aerosols and Land-Ecosystems (HI-SCALE) field campaign in 2016. In order to study the impacts of large-scale advections on the cloud populations and land-atmospheric coupling, two sets of high-resolution simulations are conducted using a Large Eddy Simulations (LES) version of the Weather Research and Forecasting Model for a selected day with transition from clear-sky to shallow precipitating clouds and then to the deep convection transition. The control simulation represents the observed clouds quite realistically. In the sensitivity experiments, large scale advections are removed to isolate its effect on the relationships of land-atmospheric interactions. In the absence of advection, it is found that 1) less organized clouds happen on the west of the domain; 2) clouds are more likely over the dry soil; and 3) rain rates increase earlier than those in the control simulation.

Using isentropic analysis and cluster analysis We show that in the absence of advection, clouds prefer to form over high sensible heat, low latent heat and low soil moisture surface. However, at about 30m, positive anomalies of equivalent potential temperature, which represents convective updraft, is preferred over low sensible heat, high latent heat and high soil moisture. Those results shed new lights on the understanding of the mechanisms of land-atmospheric interactions and convection initiations.