Observed Dawn and Twilight Pressure Sudden Peaks in the Global Martian Surface and Possible Relationships With Atmospheric Tides

Multilanders and rovers on Mars have observed the diurnal variation in surface pressure with two significant peaks at dawn and twilight (around 8:00 a.m. and 8:00 p.m.) at different locations near the equinox. The Dynamic Meteorology Laboratory Martian General Circulation Model (GCM) simulates similar phase-locked surface pressure fluctuations. The surface pressure peaks at a certain local time occur at most mid- and low-latitude locations, as GCM simulations suggested. By reconstructing the surface pressure variation from the horizontal mass flux obtained in the GCM simulations, we find that the pressure fluctuations are due to the diurnal variation in the horizontal wind divergence and convergence in the Martian tropical troposphere. The diurnal variation in surface pressure corresponds to the migrating diurnal tidal wind, with the enhanced convergence due to the overlap of the 4-hr and 6-hr tides before 8:00 a.m. and 8:00 p.m. Although the amplitudes of the 4-hr and 6-hr tides are smaller than those of diurnal tides, the convergences/divergences caused by the 4-hr/6-hr tidal winds at different altitudes are in phase and added up together to create a mass flux comparable to that induced by diurnal/semidiurnal components and lead to rapid pressure fluctuations. The 4-hr/6-hr tidal amplitudes and the two pressure peaks at dawn and twilight are the strongest near the equinox.