Variations in Vertical CO/CO₂ Profiles in the Martian Mesosphere and Lower Thermosphere Measured by the ExoMars TGO/NOMAD: Implications of Variations in Eddy Diffusion Coefficient

Yoshida, Nao; Nakagawa, Hiromu; Aoki, Shohei; Erwin, Justin; Vandaele, Ann Carine; Daerden, Frank; Thomas, Ian; Trompet, Loïc; Koyama, Shungo; Terada, Naoki; Neary, Lori; Murata, Isao; Villanueva, Geronimo; Liuzzi, Giuliano; Lopez‐Valverde, Miguel Angel; Brines, Adrian; Modak, Ashimananda; Kasaba, Yasumasa; Ristic, Bojan; Bellucci, Giancarlo; López‐Moreno, José Juan and Patel, Manish (2022). Variations in Vertical CO/CO₂ Profiles in the Martian Mesosphere and Lower Thermosphere Measured by the ExoMars TGO/NOMAD: Implications of Variations in Eddy Diffusion Coefficient. Geophysical Research Letters, 49(10), article no. e2022GL098485.

DOI: https://doi.org/10.1029/2022gl09848

Abstract

Using the Nadir and Occultation for MArs Discovery instrument aboard Trace Gas Orbiter, we derived the CO/CO₂ profiles between 75 and 105 km altitude with the equivalent width technique. The derived CO/CO₂ profiles showed significant seasonal variations in the southern hemisphere with decreases near perihelion and increases near aphelion. The estimation of the CO/CO₂ profiles with a one‐dimensional photochemical model shows that an altitude‐dependent eddy diffusion coefficient better reproduces the observed profiles than a vertically uniform one. Our estimation suggests that the eddy diffusion coefficient in L_s = 240–270 is uniformly larger by a factor of ∼2 than that in L_s = 90–120 in the southern hemisphere, while they are comparable in the northern hemisphere. This fact demonstrates that the eddy diffusion coefficient is variable with season and latitude.

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