Aerosols and tides in the martian tropics during southern hemisphere spring equinox from Mars Climate Sounder data

Abstract

We analyze Mars Climate Sounder temperature and aerosol data in the tropics to study atmospheric tides and their relation to the dust and water ice distributions. Our results from data covering Mars years (MY) 29-35 reveal that MY29 has large amplitude non-migrating thermal tides during southern hemisphere spring equinox that are not observed at the same local time in any other year. It is the nighttime temperatures that are most perturbed compared to other years, with strong temperature inversions at 35-55 km altitude. Analysis of data at different local times reveals that the temperatures and water ice clouds at 03:45 am in MY29 more closely resemble those at 05:00 am in other years, suggesting there was a shift in the phase of the diurnal tide to an earlier local time. This phase shift, and the large amplitude non-migrating thermal tides, appear to be related to early dust activity. Two early dust storms occurred in MY29 around the time there was upwelling over the tropics, associated with the Hadley circulation, enabling the dust to be transported to higher altitudes where it has a larger radiative influence. As well as dust, water ice clouds are also found to influence the tidal structure. Due to the interaction of non-migrating tides, water ice clouds occur in two discrete longitudinal regions at night. The increased radiative cooling results in increased downwelling above the clouds, leading to increased adiabatic warming and a strengthening the temperature inversions.