Thermal Structure of the Middle and Upper Atmosphere of Mars From ACS/TGO CO₂Spectroscopy

Abstract

Temperature and density in the upper Martian atmosphere, above ∼100 km, are key diagnostic parameters to study processes of the species' escape, investigate the impact of solar activity, model the atmospheric circulation, and plan spacecraft descent or aerobraking maneuvers. In this paper, we report vertical profiling of carbon dioxide (CO2) density and temperature from the Atmospheric Chemistry Suite (ACS) solar occultations onboard the ExoMars Trace Gas Orbiter. A strong CO2 absorption band near 2.7 μm observed by the middle infrared spectrometric channel (ACS MIR) allows the retrieval of the atmospheric thermal structure in an unprecedentedly large altitude range, from 20 to 180 km. We present the latitudinal and seasonal climatology of the thermal structure for 1.5 Martian years (MYs), from the middle of MY 34 to the end of MY 35. The results show the variability of distinct atmospheric layers, such as a mesopause (derived from 70 to 145 km) and homopause, changing from 90 to 100 km at aphelion to 120–130 km at perihelion. Some short‐term homopause fluctuations are also observed depending on the dust activity.

Seasonal Enhancement in Upper Atmospheric D/H at Mars Driven by Both Thermospheric Temperature and Mesospheric Water

“…Additional seasonal effects that we exclude may add nuance. Studies have demonstrated variability in the height of the homopause (Belyaev et al., 2022; Slipski et al., 2018) and mesospheric temperature (Gupta et al., 2022; Jain et al., 2023; Slipski et al., 2018) throughout the martian year. If included in our model, enhancements in both of these parameters during the perihelion season would likely both slightly suppress the diffusion of H and resulting escape, competing with the escape enhancement caused by the extra supply of atoms in the mesosphere.…”

Climatological Gravity Waves in the Middle and Upper Atmosphere of Mars Based on ACS/TGO Observations

“…Therefore, we expect that the variation of the height of the peak GW perturbations with solar longitude should be similar to the seasonal pattern of the wave turbopause. In fact, Belyaev et al (2022) found significant seasonal variability in the homopause due to the influence of atmospheric aerosol loading, rising from 90 to 100 km at aphelion to 120-130 km at perihelion. This is consistent with the seasonal variation characteristics of the height of the strongest GW perturbations, suggesting that GW activity has a very important influence on the thermal structure of the Martian middle atmosphere.…”

“…In this study, we directly used temperature data retrieved by Belyaev et al (2022) with ACS/MIR observations, including 568 vertical profiles. The time period is from 2018 May to 2021 January, corresponding to 1.5 Martian years (MYs), from L s = 181°for MY34 to L s = 355°for MY35.…”

“…The time period is from 2018 May to 2021 January, corresponding to 1.5 Martian years (MYs), from L s = 181°for MY34 to L s = 355°for MY35. Details of the retrieval scheme for atmospheric temperature can be found in the paper by Belyaev et al (2022). In order to derive both the density and temperature at a given altitude, they used a multiiterative scheme that fits a modeled transmission spectrum to the measured one.…”

Climatology of gravity wave activity based on two Martian years from ACS/TGO observations

“…The MIR spectrometer of the Atmospheric Chemistry Suite (ACS) experiment on board the Trace Gas Orbiter (TGO; Korablev et al 2018) allows for this gap in the knowledge of atmospheric variability to be filled by measuring vertical profiles of density and temperature between 20 and 160-180 km in the Martian atmosphere (Belyaev et al 2022). The algorithm of retrieving GW profiles and their characteristics, together with the first results of its application, have been presented in detail in the work by Starichenko et al (2021).…”