The Impact of Land Surface Heterogeneity on Shallow Clouds over the ARM SGP site

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Description

We aim to quantify the impact of land surface heterogeneity on mean properties of atmospheric boundary layer and non-precipitating shallow clouds averaged over horizontal scales typical of current-generation global and regional climate model grid boxes. We employ the WRF model in a nested large-eddy simulation (LES) set-up to achieve realistic simulation of summertime shallow convection over the ARM SGP site. The innermost model domain, with a horizontal size of ~30 km and horizontal resolution of 100 m, is nested within two successively coarser-resolution domains that are in turn driven by NAM 3-hourly forcing. In the control simulations, the atmospheric component of WRF is directly coupled to the NOAH land surface model in all three domains. In the experimental simulations, the surface fluxes are horizontally averaged over (i) the innermost domain, (ii) the two inner domains, or (iii) all three domains when the land surface model is coupled to the atmospheric component. By comparing the boundary-layer and cloud properties in the control and experimental simulations, we can examine in details the impact of land-surface heterogeneity with scales smaller than the horizontal scale over which the averaging algorithm is applied. Three cases of shallow convection at the ARM SGP site with different wind conditions and boundary-layer thermodynamic structures are investigated. The results from these nested-domain simulations are interpreted with the help of periodic-domain LES simulations forced with idealized surface heterogeneity patterns and prescribed wind conditions.