Aerosols and tides in the tropical martian atmosphere from Mars Climate Sounder data

Abstract:

Thermal tides are global-scale oscillations of atmospheric temperature, pressure and wind, which can influence the transport and phase of aerosols, and propagate into the upper atmosphere. The Mars Climate Sounder (MCS) instrument provides vertical profiles of temperature, dust and water ice up to ~80 km, which can be used to study thermal tides. Previous analysis has mostly focused on data at two local times, but MCS occasionally performed scanning that allowed observations at six local times per day. We use Fourier analysis on the daytime and nighttime tropical temperature profiles to investigate how the tides change over periods of ~3 hours, and whether they are linked to variations in the aerosol distribution.

Large-amplitude tides are seen in the tropics in Mars Year (MY) 29 using 3 am/pm data between Ls = 180-210°. These tides are located mostly in the northern tropics and are not seen in MY30-34 at the same local times. Studying the daytime and nighttime temperatures from MCS shows that the tides are mostly caused by longitudinal variations in nighttime temperatures. Prominent inversions occur to the east of Tharsis and south west of Isidis Planitia, which are linked to longitudinal variations in dust and water ice. The unusual tides in the northern tropics seems related to increased dust in the region, due to the early dust activity in MY29.

When looking at data taken at local times ~2 hours later at 5 am/pm, some large amplitude tides do appear in MY30-34. The appearance of these tides is related to increased water ice opacities as night progresses. Tide signatures in the tropics throughout southern spring and summer can be related to nighttime temperature inversions, which occur after regional dust storms. This suggests that the increased dust is impacting the locations of water ice clouds, with the dust and ice in turn impacting the migrating diurnal and semidiurnal tides. The interaction of these tides with the topography results in the observed strengthening of the non-migrating tides.