Aerosols and Tides in the Martian Tropics During Southern Hemisphere Spring Equinox From Mars Climate Sounder Data

We analyze Mars Climate Sounder temperature and aerosol data in the tropics, and use Fourier analysis at different local times to study atmospheric tides and their relation to the dust and water ice distributions. Our results reveal that Mars year (MY) 29 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. The nighttime temperatures are the most perturbed compared to other years, with strong temperature inversions at 35-55 km altitude. The nighttime water ice cloud structure is strongly influenced by the eastward-propagating diurnal Kelvin waves 1 and 2. Increased nighttime radiative cooling from regions of thicker clouds results in stronger downwelling above the clouds, leading to increased adiabatic warming and a strengthening of the temperature inversions. The temperatures and water ice clouds at 3:45 a.m. in MY29 more closely resemble those at 5:00 a.m. in other years, suggesting there was a shift in the phase of the diurnal tide. 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. This likely enabled the dust to be transported to higher altitudes where it has a larger radiative influence. The early dust activity in MY29 also increased the strength of the westward-propagating non-migrating thermal tides.