Capturing the Effects of Surface Flux Heterogeneity on the Lower
Sub-grid Atmosphere in Earth System Models with a Multi-Column Approach
Abstract
Earth System Models (ESMs) traditionally operate at large horizontal
resolutions, on the order of 100 km, which can obscure the effects of
smaller scale heterogeneity. When examining land surface states and
fluxes in ESMs, one common approach to mitigate this issue is to divide
the sub-grid land surface into distinct homogeneous clusters and then
resolve the water, energy, and biogeochemical processes on each cluster
or tile. The literature, as well as work in the Coupling of Land and
Atmospheric Subgrid Parameterizations (CLASP) project, indicates that
surface heterogeneity has important implications for atmospheric
processes as well. Previous work using large-eddy simulation (LES) shows
that spatial variability in surface heating can produce significant
secondary circulations closely related to the type and scale of
heterogeneity that are not captured by single column models. This
presentation aims to address this persistent weakness by using a
clustering or tiling approach, similar to that used with land surface
processes, for the atmosphere. To accomplish this task, we run the Cloud
Layers Unified By Binomials (CLUBB) single column model, a sub-grid
turbulence and cloud parameterization scheme, over a 100 km box centered
at the Southern Great Plains site in Oklahoma for a variety of surface
and atmospheric conditions. The model is run independently over multiple
surface clusters defined by surface sensible heat fluxes in the given
domain. Results indicate that significant differences exist for some
cases between the single column and multicolumn cases for liquid water
path (LWP) as well as the turbulent kinetic energy (TKE) budget, and
that results converge on consistent results with a fairly low number of
clusters (i.e., atmospheric columns). We follow this up with a connected
multicolumn setup where each column is dynamically connected with the
other columns throughout the run to qualitatively capture the
circulations observed in the LES output. The existing results show
promise for capturing the effects of subgrid scale surface flux
heterogeneity on the lower atmosphere in ESMs with the application of a
multicolumn CLUBB setup.