Large Eddy Simulations of the Dusty Martian Convective Boundary Layer With MarsWRF. Issue 9 (1st September 2021) - Wu, Zhaopeng
Abstract: Large eddy simulation (LES) of the Martian convective boundary layer (CBL) with a Mars‐adapted version of the Weather Research and Forecasting model is used to examine the impact of aerosol dust radiative‐dynamical feedbacks on 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 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 exists between 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. Plain Language Summary: We use a very high‐resolution atmospheric model (Mars‐adapted version of the Weather Research and Forecasting model) to study the interaction between dust and turbulent motions at the bottom of the Martian atmosphere. The model is validated against satellite observations and previously validated model results. Two types of experiment are conducted to test the effect of the horizontal dust distribution. With horizontally uniform dust levels, increasing the total dust amount reduces solar heating reaching the surface and thus cools the surface and weakens upward motions. However, if the dust is allowed to move horizontally in the region, upward‐moving air tends to concentrate the dust and these plumes hence become dustier than average. Dust contained in the upward plumes is then heated by the Sun, increasing the speed of upward motion. Thus, the stronger temperature differences may result in faster upward plumes as the amount of atmospheric dust increases. Stronger vertical plumes require stronger horizontal motions at the surface, due to mass conservation within a convection cell. These stronger surface winds may lead to greater dust lifting, and thus this study suggests that dust storms on Mars may grow in their early stages through a natural positive feedback between dust inhomogeneity, radiative heating, and accelerated winds. Key Points: Dust radiative‐dynamical feedback upon turbulent mixing in the Martian convective boundary layer is demonstrated by Large Eddy Simulation The destabilizing effect of dust lateral heating contrasts is found to augment convection and deepen the boundary layer Under some circumstances a positive feedback may exist between dust radiative heating, the intensity of boundary layer mixing, and dust lifting