Gravity wave activity in the Martian atmosphere from the ACS solar occultation experiment on board ExoMars/TGO

Gravity waves (GWs) are omnipresent in planetary atmospheres and originate from displacements of air parcels. Since they re-distribute energy and momentum between atmospheric layers, GWs greatly affect atmospheric dynamics. In our work, we study the parameters [1] of GWs and their vertical distributions in the Martian atmosphere. In order to retrieve those parameters we process temperature vertical profiles retrieved from the Atmospheric Chemistry Suite (ACS)/Trace Gas Orbiter (TGO) [2] solar occultation measurements. We determine and analyze such characteristics of GWs as amplitude, acceleration (wave drag), vertical flux of horizontal momentum, potential energy­­­­­_­­.

We observe the symmetrical distribution of GW activity during the Martian equinoxes, while during solstices the activity is prevailing over winter hemisphere. Maxima of the wave drag is coinciding with the areas of the weak zonal wind, which is retrieved from the MAOAM Martian general circulation model (MGCM) [3]. During the MY34 global dust storm, GW activity decreased in the northern hemisphere below 80 km and increased above this height in the high-latitude northern latitudes. This behavior agrees with previous observations and simulations, while the increase of wave activity in the southern polar latitudes below 80 km was not previously observed or predicted [4].

ACS is a part of the TGO, which represents the ESA-Roscosmos ExoMars 2016 collaborative mission. The instrument consists of three infrared channels [1]: near-IR (NIR, 0.73-1.6 µm), middle-IR (MIR, 2.3-4.2 µm) and thermal-IR (TIRVIM, 1.7-17 µm). In this work, we use the data obtained from the MIR and NIR instruments, operating in solar occultation mode since April 2018. Both spectrometers allow to retrieve vertical temperature and density profiles from the CO2 transmission spectra in the altitude range of 10-180 km (MIR) [5], 10-100 km (NIR) [6]. Presently, we report the observations for 3 Martian years (MY), from the middle of MY34 (April 2018) to the end of MY37 (November 2024), counting ~1100 occultations of MIR and ~12300 occultations of NIR. 

The research is supported by the grant from the RSF #25-22-00494, https://rscf.ru/project/25-22-00494/

[1] Starichenko E. et al., 2021. Gravity wave activity in the Martian atmosphere at altitudes 20–160 km from ACS/TGO occultation measurements. Journal of Geophysical Research: Planets, 126, e2021JE006899. DOI: 10.1029/2021JE006899

[2] Korablev O., Montmessin F., and ACS Team, 2018. The Atmospheric Chemistry Suite (ACS) of three spectrometers for the ExoMars 2016 Trace Gas Orbiter. Space Sci. Rev., 214:7. DOI 10.1007/s11214-017-0437-6.

[3] Medvedev, A. S., & Hartogh, P. (2007). Winter polar warmings and the meridional transport on Mars simulated with a general circulation model. Icarus, 186 , 97– 110.

[4] Starichenko E. D., Medvedev A. S., Belyaev D. A., et al. Climatology of gravity wave activity based on two Martian years from ACS/TGO observations. Astronomy&Astrophysics, 683, A206 (2024). https://doi.org/10.1051/0004-6361/202348685

[5] Belyaev D. et al., 2022. Thermal Structure of the Middle and Upper Atmosphere of Mars from ACS/TGO CO2 Spectroscopy. Journal of Geophysical Research: Planets. 127, e2022JE007286. doi: 10.1029/2022JE007286

[6] Fedorova A. et al., 2022. A two-Martian year survey of the water vapor saturation state on Mars based on ACS NIR/TGO occultations. Submitted to Journal of Geophysical Research: Planets. 128, e2022JE007348. doi: 10.1029/2022JE007348