Thermal Structure of the Middle and Upper Atmosphere of Mars from ACS/TGO CO2 Spectroscopy

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 (TGO). 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 a 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 150 km) and homopause, changing from 80-90 km at aphelion to 100-110 km at perihelion. Some short-term homopause fluctuations are also observed depending on the dust activity.

Climatology of Gravity Wave Activity From Two Martian Years of ACS/TGO Observations

“…In this work, we use the data obtained from the MIR and NIR spectrometric channels operating in the solar occultation mode since April 2018. ACS-MIR is a cross-dispersion echelle spectrometer that allows for retrieving temperature and density vertical profiles in the strong 2.7 µm CO 2 absorption band covering the broad altitude range of 20-180 km (Belyaev et al, 2021(Belyaev et al, , 2022. ACS-NIR, an echelle spectrometer combined with an acousto-optic tunable filter, measures the atmospheric structure in 1.43 µm and 1.57 µm CO 2 bands at altitudes from 10 to 100 km (Fedorova et al, 2020(Fedorova et al, , 2023.…”

“…The procedures of retrieving density and temperature vertical profiles from the transmission spectra of CO 2 are extensively described in the papers of Belyaev et al (2021Belyaev et al ( , 2022 for the MIR channel and of Fedorova et al (2020Fedorova et al ( , 2023 for the NIR channel. Profiles with estimated 1-σ errors exceeding 20 K have been removed from consideration based on expected wave amplitudes.…”

“…Profiles with estimated 1-σ errors exceeding 20 K have been removed from consideration based on expected wave amplitudes. Validation between simultaneously measured MIR and NIR profiles demonstrates a good coincidence below 100 km with dispersion of 5-10 K in more than 90% of occultations (Belyaev et al, 2022). When retrieving the GW parameters (see Section 3), the data were checked for reasonably smooth background temperature profiles (suitable for extracting waves) and for adequate values of the potential energy (<1000 J kg −1 ).…”

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

“…The data sets generated by the ExoMars Trace Gas Orbiter instruments analyzed in this study are available in the ESA Planetary Science Archive (PSA) repository, https://archives.esac.esa.int/psa/%23%21Table%20View/ACS%3Dinstrument, following a 6 months prior access period, following the ESA Rules on Information, Data, and Intellectual Property. The data products generated in this study (retrieved CO 2 density and temperature distributions) are available on Belyaev (2022).…”

Thermal Structure of the Middle and Upper Atmosphere of Mars from ACS/TGO CO2 Spectroscopy

“…ACS%3Dinstrument, following a 6 months prior access period, following the ESA Rules on Information, Data, and Intellectual Property. The data products generated in this study (retrieved CO 2 density and temperature distributions) are available on Belyaev (2022).…”