Semi-coupling of a Field-scale Resolving Land-surface Model and WRF-LES
to Investigate the Influence of Land-surface Heterogeneity on Cloud
Development
Abstract
Contemporary Earth system models mostly ignore the sub-grid scale (SGS)
heterogeneous coupling between the land surface and atmosphere. To aid
in the development of coupled land and atmosphere SGS parameterizations
for global models, we present a study of different aspects of
highly-realistic sub-100 km scale land-surface heterogeneity. The
primary experiment is a set of simulations of September 24, 2017 over
the Southern Great Plains (SGP) site using the Weather Research and
Forecasting (WRF) model with 100-m horizontal resolution. The overall
impact of land-surface heterogeneity is evaluated by comparing cloud and
turbulent kinetic energy (TKE) production in large-eddy simulations
(LESs) using heterogeneous and homogeneous surface fields (namely
sensible and latent heat fluxes) specified by an offline field-scale
resolving land-surface model (LSM). The heterogeneous land surface leads
to significantly more cloud and TKE production. We then isolate specific
sources of heterogeneity by using selectively domain-wide averaged
fields in the LSM. It is found that heterogeneity in the land surface
created by precipitation is effectively responsible for the increases in
cloud and TKE production, while rivers and soil type have a negligible
impact and land cover has only a small impact. Additional experiments
modify the Bowen ratio in the surface fields and the initial wind
profile of the heterogeneous case to clarify the results seen. Finally
two additional days at the SGP site are simulated showing a similar
increase in cloud production in heterogeneous cases.