Meteorology of proposed Mars Exploration Rover landing sites

Abstract

A descriptive study of the near‐surface meteorology at three of the potential Mars Exploration Rover (MER) landing sites (Terra Meridiani, Gusev Crater, and Melas Chasma) is presented using global and mesoscale models. The mesoscale model provides a detailed picture of meteorology on scales down to a few kilometers but is not well constrained by observations away from the Viking and Pathfinder landing sites. As such, care must be taken in the interpretation of the results, with there being high confidence that the types of circulations predicted will indeed occur and somewhat less in the quantitative precision of the predictions and the local‐time phasing of predicted circulations. All three landing sites are in the tropics and are affected by Hadley circulation, by diurnal variations due to the global thermal tide, and by planetary scale topography (in these particular cases from Tharsis, Elysium, and the global topographic dichotomy boundary). Terra Meridiani is least affected by large variations in local topography. Mean winds at Terra Meridiani during MER landing would be less than 10 m/s with little vertical shear. However, these low wind speeds result from strong mixing in the early afternoon convective boundary layer, which creates its own hazard in the horizontal variation of vertical winds of up to 8 m/s (both upward and downward). In Gusev Crater the topography of Ma'adim Vallis and the crater rim generates strong diurnally reversing channeling of wind in Ma'adim Vallis and diurnally reversing radial flow in the crater associated with thermal slope winds on the crater rim. The overturning circulation in Gusev Crater slightly suppresses the daytime convective boundary layer. Melas Chasma in Valles Marineris provides an example of strong topographic forcing of near‐surface circulation. Of particular interest is the channeling of regional scale wind toward the center of the Tharsis plateau during the evening. This results in a surface level jet along the canyon of over 25 m/s. Drainage of air from the plateau and into the canyon produces vertical winds down the canyon walls in the evening of over 5 m/s. In contrast, during the early afternoon (MER landing time), horizontal winds at the proposed MER landing site are relatively calm, with little mean shear with height. This results from the proposed site being in a region of local divergence and the action of daytime convection. The nature of flow in Melas Chasma results in an interesting dual maximum in boundary convection and depth, with the usual daytime afternoon free convective maximum being joined by a mechanically forced nighttime boundary layer of almost 2 km depth.