Variations in the Depth of the Convective Boundary Layer on Mars

Radio occultation experiments conducted with Mars Express are providing unique information about the structure and dynamics of the martian lower atmosphere. We focus on two sets of observations obtained during northern spring in successive martian years (MY 27 and 28). These experiments sampled the tropics at local times in late afternoon, 15-17 h, with broad coverage in latitude and longitude. Most of the atmospheric profiles retrieved from these data contain a well-mixed convective boundary layer (CBL), which is easily resolved by radio occultation measurements. We have analyzed these profiles to determine properties such as the depth of the CBL, the potential temperature within the convective layer, and their spatial variations. There are more similarities than differences between the observations from the two years. In both cases the depth of the CBL is clearly correlated with variations in surface elevation on planetary scales (e.g. Hinson et al., Icarus 198, 57-66, 2008). In general, the CBL is deep (8-10 km) where the surface elevation is high, as in Tharsis Montes and Syrtis Major, and shallow (4-6 km) where the surface elevation is low, as in Amazonis and Utopia. The elevation at the top of the CBL varies with longitude by more than 10 km (at fixed local time), resulting in strong zonal modulation in the vertical mixing of dust, water vapor, heat, and momentum. The spatial sampling of the two sets of observations is highly complementary, yielding more complete characterizations of the structure of the CBL in select locations, such as in and around Isidis Planitia.