Observed dawn and twilight pressure fluctuation in the global Martian
surface and possible relationships with atmospheric tides
Abstract
Insight and other observations of the Martian surface at different
locations have recorded the diurnal variation in surface pressure (Ps)
with two rapid fluctuations that occur at dawn and dusk (around LT0800
and LT2000). These short-period surface pressure perturbations at
specific local times are typically observed near Martian equinox.
Similar phase-locked surface pressure fluctuations over most areas of
the middle and low latitudes are simulated by the Martian General
Circulation Model at the Dynamic Meteorology Laboratory (LMD). This
phenomenon is thus likely to be global rather than local. By
reconstructing the surface pressure variation from the horizontal mass
flux, the pressure fluctuations in a sol can be attributed to the
diurnal variation in the horizontal wind divergence and convergence in
the Martain tropical troposphere in the GCM simulations. The background
diurnal variation in Ps is related to the diurnal migrating tidal wind,
while the enhanced convergence due to the overlap of the 4-hour and
6-hour tides before LT0800 and LT2000 is responsible for the Ps peaks
occurring at dawn and twilgith. Although the amplitudes of the 4-hour
and 6-hour tides are smaller than those of diurnal tides, the phases of
these tides remain similar in the Martain troposphere, which suggests
that the convergences and divergences due to 4 h/6 h tidal winds at
different altitudes are in phase and together create a mass flux
comparable to that induced by diurnal/semidiurnal components and lead to
rapid pressure fluctuations.