A new model to simulate the Martian mesoscale and microscale atmospheric circulation: Validation and first results

Abstract

The Laboratoire de Météorologie Dynamique (LMD) Mesoscale Model is a new versatile simulator of the Martian atmosphere and environment at horizontal scales ranging from hundreds of kilometers to tens of meters. The model combines the National Centers for Environmental Prediction(NCEP)‐National Center for Atmospheric Research (NCAR) fully compressible nonhydrostatic Advanced Research Weather Research and Forecasting (ARW‐WRF) dynamical core, adapted to Mars, with the LMD‐general circulation model (GCM) comprehensive set of physical parameterizations for the Martian dust, CO2, water, and photochemistry cycles. Since LMD‐GCM large‐scale simulations are also used to drive the mesoscale model at the boundaries of the chosen domain of interest, a high level of downscaling consistency is reached. To define the initial state and the atmosphere at the domain boundaries, a specific “hybrid” vertical interpolation from the coarse‐resolution GCM fields to the high‐resolution mesoscale domain is used to ensure the stability and the physical relevancy of the simulations. Used in synoptic‐scale mode with a cyclic domain wrapped around the planet, the mesoscale model correctly replicates the main large‐scale thermal structure and the zonally propagating waves. The model diagnostics of the near‐surface pressure, wind, and temperature daily cycles in Chryse Planitia are in accordance with the Viking and Pathfinder measurements. Afternoon gustiness at the respective landing sites is adequately accounted for on the condition that convective adjustment is turned off in the mesoscale simulations. On the rims of Valles Marineris, intense daytime anabatic (∼30 m s−1) and nighttime katabatic (∼40 m s−1) winds are predicted. Within the canyon corridors, topographical channeling can amplify the wind a few kilometers above the ground, especially during the night. Through large‐eddy simulations in Gusev Crater, the model describes the mixing layer growth during the afternoon, and the associated dynamics: convective motions, overlying gravity waves, and dust devil–like vortices. Modeled temperature profiles are in satisfactory agreement with the Miniature Thermal Emission Spectrometer (Mini‐TES) measurements. The ability of the model to transport tracers at regional scales is exemplified by the model's prediction for the altitude of the Tharsis topographical water ice clouds in the afternoon. Finally, a nighttime “warm ring” at the base of Olympus Mons is identified in the simulations, resulting from adiabatic warming by the intense downslope winds along the flanks of the volcano. The surface temperature enhancement reaches +20 K throughout the night. Such a phenomenon may have adversely affected the thermal inertia derivations in the region.