Ter‐Diurnal Atmospheric Tide on Mars.

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 Ls 230° dust storm is not detected by either platforms. During global dust storms, MSL, VL1, and VL2 detect their highest amplitudes. The GCM predicts the weakest amplitudes at the equinoxes, while the strongest ones are predicted in summer for both hemispheres. GCM amplitudes tend to differ from the observations but match slightly better around the aphelion season. During this time, model results suggest that the two most prominent modes are the sun‐synchronous ter‐diurnal tide and an eastward propagating resonantly enhanced Kelvin wave. 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. Plain Language Summary: Atmospheric pressure is a crucial meteorological parameter, since many weather phenomena on Mars, such as the condensation and sublimation of the seasonal polar caps, global scale atmospheric tides, and local turbulent flows, are associated with changes in surface pressure. On a diurnal time scale, atmospheric tides dominate surface pressure daily variations in the Martian tropics. They are generated by the diurnally varying solar radiation and additionally modified by topography, surface properties, and atmospheric absorbers. Here, we use pressure observations from Mars Science Laboratory, InSight, Viking lander 1, and 2 to characterize the Martian atmospheric tide that has a period of 8 hr, known as the ter‐diurnal tide, and compare results with model simulations. The results show that the Mars Science Laboratory and InSight observe similar seasonal cycles for the amplitude and phase of the ter‐diurnal tide. In addition, both these platforms react similarly to atmospheric dust content. The Viking landers and Mars Science Laboratory observe their highest amplitudes during the global dust storms. We find that modeled amplitudes are the strongest during summertime for both hemispheres and typically lower than those observed throughout the year. Moreover, the ter‐diurnal tide may be significantly affected by water ice clouds. Key Points: We analyze the ter‐diurnal atmospheric tide from pressure observations at four surface stations and compare them with model predictionsModel and observations suggest a clear wavenumber 6 amplitude and phase patterns in longitude at northern hemisphere (NH) summerThis study suggests the ter‐diurnal component's sensitivity to water ice clouds and a resonantly enhanced Kelvin wave near the NH summer solstice [ABSTRACT FROM AUTHOR]