  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.
