The Impact of Surface Heterogeneity on Surface Flux Estimates of the Stable Boundary Layer Using Single Column Modeling

Abstract

The surface fluxes of momentum and heat play an important role in the evolution of the atmospheric boundary layer (ABL). Accurate representation of the fluxes in weather and climate forecasting models, especially when dealing with heterogeneous land surfaces. This is complicated under stable conditions where the fluxes are often smaller in magnitude and turbulence cannot be relied on to mix out the heterogeneity effects. Here the role of surface heterogeneity in determining the average surface fluxes is investigated through the development of a single column model (SCM) in Python. The SCM features some of the most popular PBL scheme currently implemented in the Weather Research and Forecasting model (WRF) as well as various surface layer (SL) parameterizations that can account for surface heterogeneity.

The SCM is validated against with three different cases with varying complexities. The first two cases, GABLS1 and GABLS2, are idealized atmospheric boundary layer studies that have been well cited in the literature. The third case used with the SCM is from a recent field project during the summer of 2021 by the Boundary Layer Integrated Sensing and Simulation (BLISS) group at the University of Oklahoma, where multiple different boundary layer observational instruments were deployed.

The role of heterogeneity on flux properties was investigated by altering the type and strength of the surface heterogeneity. Both surface temperature heterogeneity and surface roughness heterogeneity are investigated with the current surface models implemented in the SCM. It was found that both types of surface heterogeneity impacted the magnitude of the surface fluxes of heat and momentum, especially under stable conditions. The surface temperature heterogeneity impacted the surface heat fluxes more significantly than the surface momentum fluxes. With surface roughness heterogeneity, the surface fluxes of heat and momentum were impacted equally. Future expansion to this work is discussed including further additions to the SCM.