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Seasonal and dust‐related variations in the dayside thermospheric and ionospheric compositions of Mars observed by MAVEN/NGIMS

Abstract : We report seasonal and dust-related variations in neutral and ion species (CO2, O, and N2, and CO2+, O2+, O+, and N+, respectively) in the dayside Martian upper atmosphere between altitudes of ∼150 and ∼250 km observed by the Neutral Gas and Ion Mass Spectrometer aboard the Mars Atmosphere and Volatile Evolution spacecraft. The sinusoidal seasonal variations in CO2+ and O2+ densities are clearly identified, while that of O+ is less discernible. These observed variations in ion densities are well reproduced by a photochemical equilibrium model for CO2+ and O+ densities when we combine them with solar cycle variations. Furthermore, we find a decrease in O, O+, and O2+ densities in the whole altitude range at Ls = 342 - 346 in MY 33 during a regional dust event. The decrease in O density would lead to decreases in O+ and O2+ densities in the ionosphere through ion-neutral reactions. Observed variations in ion and neutral species associated with the season and a regional dust storm are also confirmed in pressure coordinates. Observations show that the CO2+/O+ ratio at a given pressure level in the ionosphere varies by a factor of ∼3, which can modify the composition of ion outflow from the Martian atmosphere.
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https://hal-insu.archives-ouvertes.fr/insu-03408265
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Submitted on : Saturday, August 6, 2022 - 9:06:22 AM
Last modification on : Sunday, August 7, 2022 - 3:39:42 AM

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Nao Yoshida, Naoki Terada, Hiromu Nakagawa, David A. Brain, Shotaro Sakai, et al.. Seasonal and dust‐related variations in the dayside thermospheric and ionospheric compositions of Mars observed by MAVEN/NGIMS. Journal of Geophysical Research. Planets, Wiley-Blackwell, 2021, 126 (11), pp.e2021JE006926. ⟨10.1029/2021JE006926⟩. ⟨insu-03408265⟩

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