Abstract
Cyclic absorption of solar radiation generates oscillations in
atmospheric fields. These oscillations are called atmospheric or thermal
tides, which are furthermore modified by topography and surface
properties. This leads to a complex mix of sun-synchronous and non
sun-synchronous tides that propagate around the planet eastward and
westward. This study focuses on analyzing the ter-diurnal component
(period of 8 hr) from surface pressure observations by Mars Science
Laboratory (MSL), InSight, Viking Lander (VL) 1, and VL2. General
Circulation Model (GCM) results are used to provide a global context for
interpreting the observed ter-diurnal tide properties. MSL and InSight
have a clear and similar seasonal cycle, with local amplitude peaks at
around solar longitude (Ls) 60◦ , Ls 130◦ and Ls 320◦ . The amplitude
peak at Ls 320◦ is related to the annual dust storm, while the dust
storm around Ls 230◦ is not detected by either platforms. During the
global dust storms, MSL, VL1, and VL2 detect their highest amplitudes.
GCM predicts the weakest amplitudes at the equinoxes, while the
strongest ones are predicted in summertime for both hemispheres. GCM
amplitudes are typically lower than observed, but match better during
the aphelion season. During this time, model results suggest that the
two most prominent modes are the sun-synchronous ter-diurnal tide (TW3)
and an eastward propagating resonantly-enhanced Kelvin wave (TE3).
Simulations with and without the effect of radiative heating by water
ice clouds indicate the clouds may play a significant role in forcing
the ter-diurnal tide during northern hemisphere summer season.