Thermal Tides in the Martian Atmosphere Near Northern Summer Solstice Observed by ACS/TIRVIM Onboard TGO

Abstract

Thermal tides in the Martian atmosphere are investigated using temperature profiles retrieved from TIRVIM nadir observations.• Diurnal tide dominates daily temperature variations; semi-diurnal tide and diurnal Kelvin wave are also important.• Observations agree well with numerical simulations, but suggest phases of diurnal and semi-diurnal tides earlier than predicted.

Migrating Thermal Tides in the Martian Atmosphere During Aphelion Season Observed by EMM/EMIRS

“…Amplitudes of diurnal and semidiurnal tides agree well with results in previous works during this aphelion season (Banfield et al 2003, Kleinböhl et al 2013, Fan et al 2022, but the phases show significant differences. The inferred amplitude of the ter-diurnal (~0.3-0.5K) is also consistent with the TIRVIM results (<0.5K, Fan et al 2022), where the data sampling scheme was not sufficiently good for detecting this mode.…”

“…Analysis in this work mainly focuses on migrating thermal tides, as they constitute the main diurnal temperature variation in the Martian atmosphere below 60 km (Banfield et al., 2003; Fan et al., 2022; Lee et al., 2009). By applying the least‐square fit of Equation to the observed temperatures (Section 2.3), amplitudes and phases of the tides are derived.…”

“…Dealiasing of these wave modes requires significant assumptions of the Martian atmospheric physical properties and knowledge from tidal theory (Lindzen & Chapman, 1969). Observations obtained by PFS and TIRVIM on slowly drifting orbits (Fan et al., 2022; Giuranna et al., 2021) have strong seasonal change influence in the interpretation of diurnal variations. The advantage of EMM/EMIRS observations that cover all geographic locations and local times within 10 days (∼5° in L S ) largely addresses this issue, which enables detailed tide investigations with good constraints on their amplitudes and phases, as well as the detection of the ter‐diurnal tide.…”

“…The temperature structure shows typical solstice features with a warm summer pole and a warming structure at a few to tens of Pa towards the winter pole, which is a result of the downwelling branch of the Hadley circulation. Comparison with the predictions of the Mars Planetary Climate Model (PCM, Forget et al 1999, Madeleine et al 2011, Forget et al 2022, where microphysics of radiatively active water clouds are included, is given in the Supporting Information (Text S3, Figure S4). The model generally agrees well with the observation except for some temperature overestimates at low latitudes by a few K, and underestimates near the poles (Figure S4f).…”

“…The least-square fit with a linear assumption has been shown successful in analyzing observations of many previous missions, e.g., MCS (Wu et al 2015(Wu et al , 2017 and TIRVIM (Fan et al 2022), despite that the unequally-spacing observations centered around two local times of MCS result in large uncertainty of the interpreted semi-diurnal tide, and that the slow local time drifting of TIRVIM data introduce seasonal variations into the diurnal analysis. In a given latitude bin (φ) and at a certain pressure level (p), the observed temperature (T) is assumed to be a function of longitude (λ) and universal time (t), so Equation (1) can be rewritten to achieve the linearity of unknowns.…”