Capturing the Effects of Surface Heterogeneity Induced Secondary Circulations on the Lower Sub-grid Atmosphere in Earth System Models

Earth System Models (ESMs) traditionally operate at large horizontal resolutions, on the order of 100km, which can obscure the effects of smaller scale heterogeneity. The literature, as well as work in the Coupling of Land and Atmospheric Subgrid Parameterizations (CLASP) project, indicates that surface heterogeneity, particularly in surface fluxes, has important implications for not only surface processes but atmospheric processes as well. Previous work using large-eddy simulation (LES) shows that spatial variability in surface heating can produce significant secondary circulations that are closely related to the type and scale of heterogeneity and are not currently captured by single column sub-grid atmospheric parameterizations used in ESMs.. This presentation aims to address this persistent weakness by using a multi-column approach, where two single column models, one over a high sensible heat flux portion of a climate gridcell domain and another over a low sensible heat flux portion, are coupled through a modeled secondary circulation. 

 

To accomplish this task, we run the Cloud Layers Unified By Binomials (CLUBB) standalone single column model over a 100 km box centered at the Southern Great Plains site in Oklahoma for a variety of surface and atmospheric conditions both as a single column model, and with two coupled columns. Results are also compared to LESs that use a homogeneous surface flux field and LESs that use realistic, high resolution surface flux fields. Initial results focus on liquid water path (LWP) response to added heterogeneity for 43 day long simulations. We observed qualitatively similar responses in LWP as a result of accounting for heterogeneity induced secondary circulations in both LES and multi-column CLUBB as well as indications of clear trends in response based on the atmospheric conditions. This work indicates that a multi-column setup has significant promise for modeling the impacts of heterogeneity induced secondary circulations for application in ESMs at a fraction of the computational expense of LES. Continuing work expands this analysis to cover a wider variety of surface and atmospheric conditions, determine when multi column CLUBB has significant sensitivities to heterogeneity induced secondary circulations, and explore avenues for further simplification of the model setup.