Ultraviolet dayglow emissions and ratios in the Mars atmosphere

peer reviewedThe Imaging UltraViolet Spectrograph (IUVS) (McClintock et al., 2015) onboard the MAVEN (Mars Atmosphere and Volatile EvolutioN) spacecraft performs limb observations of the Mars atmosphere in the dayside. Spectra have been acquired in the ultraviolet domain, between and 110 and 340 nm, since September 2014.Additionally, the UVIS (UV and Visible Spectrometer) channel of the NOMAD (Nadir and Occultation for MArs Discovery) spectrometer (Patel et al., 2017; Vandaele et al., 2018) onboard the ExoMars Trace Gas Orbiter has performed the same type of observations both in the middle ultraviolet and the visible domains (200 - 650 nm), since April 2019. It is the first instrument that allows studying UV and visible emissions simultaneously that can, thus, be directly compared.The visible emissions of the oxygen green line (557.7 nm, Gérard et al., 2020) and the oxygen red line doublet (630.0-636.4 nm, Gérard et al., 2021) have already been investigated by Soret et al. (2022), using the NOMAD/UVIS data. The variation of their peak brightness and altitudes have been studied over seasons and compared to photochemical model simulations.In this work, we present the ultraviolet dayglow counterpart of the visible dayglow and compare the results of both the NOMAD/UVIS and MAVEN/IUVS instruments.The [OI] 297.2 nm emission that, like the oxygen green line, originates from the O(1S) state is analyzed. The [OI] 297.2 nm has already been extensively studied with the IUVS instrument (Gkouvelis et al., 2018) but it is the first time that both the 297.2 and 557.7 nm can be observed simultaneously, with NOMAD/UVIS. The correlation of those emissions is shown and the ratio I(557.7 nm)/I(297.2 nm) is established with NOMAD/UVIS concurrent measurements.The CO2+ UVD and CO Cameron bands, that have been studied with the MAVEN/IUVS instrument are also presented and compared to UVIS observations. Finally, the CO2+ Fox-Duffendack-Barker (FDB) system, that has not been observed on Mars since Mariner, is also investigated. We present averaged limb profiles of all these ultraviolet emissions, their seasonal variations and ratios of their brightness. References: Gérard, J. C. et al. (2020), Detection of green line emission in the dayside atmosphere of Mars from NOMAD-TGO observations. Nature Astronomy, 4(11), 1049-1052Gérard, J. C. et al. (2021), First observation of the oxygen 630 nm emission in the Martian dayglow. Geophysical Research Letters, 48(8), e2020GL092334, https://doi.org/10.1029/2020GL092334Gkouvelis, L., et al. (2018), The O(1S) 297.2-nm dayglow emission: a tracer of CO2 density variations in the Martian lower thermosphere. Journal of Geophysical Research: Planets, 123(12), 3119-3132McClintock, W. E. et al. (2015), The Imaging Ultraviolet Spectrograph (IUVS) for the MAVEN mission. Space Science Reviews, 195(1-4), 75-124. https://doi.org/10.1007/s11214-014-0098-7Patel, M. R. et al. (2017), NOMAD spectrometer on the ExoMars trace gas orbiter mission: part 2—design, manufacturing, and testing of the ultraviolet and visible channel. Applied optics, 56(10), 2771-2782. https://doi.org/10.1364/AO.56.002771Soret, L. et al. (2022), The Mars oxygen visible dayglow: a Martian year of NOMAD/UVIS observations, Journal of Geophysical ResearchVandaele, A. C. et al. (2018), NOMAD, an integrated suite of spectrometers for the ExoMars Trace Gas Mission: Technical description, science objectives, and expected performance. Space Science Reviews, 214(5). https://doi.org/10.1007/s11214-018-0517-