PNNL

Abstract

Land-atmosphere interactions and boundary layer processes play important roles in the formation of shallow clouds and their potential transition to deep convective precipitation over the Southern Great Plains. In this study, we investigate multiple scale processes associated with surface heterogeneity of soil moisture induced convective clouds observed during the 2016 Holistic Interactions of Shallow Clouds, Aerosols, and Land-Ecosystems (HI-SCALE) field campaign. Analysis on isentropic coordinates enabled the tracking of circulations that transport energy upward and to capture the core convective processes induced by land heterogeneity. The isentropes associated with upward motion are found to connect the ground with high latent heat regions to cloud bases directly over high sensible heat regions, while isentropes associated with downward motion connect precipitation to the ground with high sensible heat regions. The mixing of dry warm parcels ascending from high sensible heat and moist parcels from high latent heat regions leads to cloud formation. We also examined the energy transport at various spatial scales and found that the turbulent scale dominates vertical energy transport. At scales larger than 27 km, convection does not transport surface energy upwards in lower boundary layer but contributes to vertical energy transport aloft. Moreover, larger soil moisture gradients lead to deeper convection at scales between 0.3 to 2.7 km and favor the upscale growth of convective clouds to scales larger than 27 km.