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
Vandaele, Ann Carine; Modak, Ashimananda; Brines, Adrian; Aoki, Shohei; Thomas, Ian; Liuzzi, Giuliano; Erwin, Justin; Yoshida, Nao; Daerden, Frank; Ristic, Bojan; Bellucci, Giancarlo; Patel, Manish; Terada, Naoki; Lopez-Valverde, Miguel Angel; Neary, Lori; Kasaba, Yasumasa; Nakagawa, Hiromu; Trompet, Loïc.; Koyama, Shungo; Murata, Isao; Villanueva, Geronimo; López-Moreno, José Juan
Japan, Belgium, United States, Spain, Italy, United Kingdom
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 Ls = 240-270 is uniformly larger by a factor of ∼2 than that in Ls = 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.