Integrating Land Surface Heterogeneity in the EDMF Scheme for Convective Boundary Layers: Insights from LES and Simplified models

Abstract:

Modeling the overland atmospheric boundary layer (ABL) in weather and climate models has traditionally relied on the two-layer approach, in which the ABL comprises a surface layer where Monin-Obukhov Similarity (MOS) theory is applicable and a mixed layer for which the Eddy Diffusivity Mass Flux (EDMF) modeling scheme has shown some merits. This approach essentially ignores the implications of heterogeneity in land surface properties (which is unresolved or subgrid scale in atmospheric models) in the ABL scheme, limiting its effect to flux aggregation (or effective parameter aggregation) from individual SGS tiles to the lowest atmospheric model height only. The work here combines a suite of large eddy simulation (LES) experiments with simplified closure models to incorporate the effects of secondary circulations between patches/tiles at the land surface on both the scaling laws of the surface layer and on mixed layer plumes. The LES experiments span a variety of spatial scales of heterogeneity (roughness lengths and thermal heterogeneity) and geostrophic wind conditions, allowing for a comprehensive examination of the effects of heterogeneity wavelength and large scale atmospheric forcing on the depth of the dynamic sublayer, blending heights, and convective plume characteristics.