Diurnal Features of Mars Reanalyses

The diurnal cycle, with its strong day-night contrast due to the low thermal inertia of the Martian atmosphere and the strong surface response to solar heating during the daytime, dominates Mars weather in many regions. The thermal tides, forced by the day-night contrast in solar heating, manifest themselves as migrating (sun-synchronous) and non-migrating variations in temperature, wind and pressure. Tides are also associated with upslope and downslope flows . Thermal tides are linked to dust through a positive feedback mechanism: stronger dust lifting results in stronger solar heating absorption and thus stronger thermal tides; the resulting surface wind stresses are important for dust lifting. For example the constructive interference of traveling waves and tide circulations can give rise to "flushing" dust storms. Spacecraft temperature observations, such as those retrieved from the Thermal Emission Spectrometer (TES), are limited to twice-daily sampling. Analyses from data assimilation provide atmospheric fields at all times of day, enabling a more comprehensive analysis of tides. Here, TES profiles are assimilated by the Local Ensemble Transfer Kalman Filter (LETKF) into the GFDL Mars Global Climate Model (MGCM). We can obtain hourly ensemble mean analysis fields by applying a no-cost smoother to the 4D-LETKF, and examine "local time" plots of temperatures, pressures, winds, and surface stresses. We will compare the tides among reanalyses and with freely running model simulations to evaluate the degree of convergence of these fields.