Large Eddy Simulations of the Dusty Martian Convective Boundary Layer
with MarsWRF
Abstract
Large eddy simulation (LES) of the Martian convective boundary layer
(CBL) with a Mars-adapted version of the Weather Research and
Forecasting model (MarsWRF) is used to examine aerosol dust
radiative-dynamical feedback upon turbulent mixing. The LES is validated
against spacecraft observations and prior modeling. To study dust
redistribution by coherent dynamical structures within the CBL, two
radiatively-active dust distribution scenarios are used—one in which
the dust distribution remains fixed and another in which dust is freely
transported by CBL motions. In the fixed dust scenario, increasing
atmospheric dust loading shades the surface from sunlight and weakens
convection. However, a competing effect emerges in the free dust
scenario, resulting from the lateral concentration of dust in updrafts.
The resulting enhancement of dust radiative heating in upwelling plumes
both generates horizontal thermal contrasts in the CBL and also
increases buoyancy production, jointly enhancing CBL convection. We
define a dust inhomogeneity index (DII) to quantify how much dust is
concentrated in upwelling plumes. If the DII is large enough, the
destabilizing effect of lateral heating contrasts can exceed the
stabilizing effect of surface shading such that the CBL depth increases
with increasing dust optical depth. Thus, under certain combinations of
total dust optical depth and the lateral inhomogeneity of dust, a
positive feedback may exist among dust optical depth, the vigor and
depth of CBL mixing, and—to the extent that dust lifting is controlled
by the depth and vigor of CBL mixing—the further lifting of dust from
the surface.