MARS OXYGEN GREEN LINE DAYGLOW FROM NOMAD/UVIS AND MODEL COMPARISON

The UVIS (UV and Visible Spectrometer) channel of the NOMAD (Nadir and Occultation for MArs Discovery) spectrometer onboard the ExoMars Trace Gas Orbiter performs limb observations of the dayside of the Mars atmosphere in both the visible and the ultraviolet domains since April 2019. The recently discovered visible emissions of the oxygen green line at 557.7 nm has here been investigated. The variations of the limb profile of this emission are studied over seasons. These average limb profiles are compared to photochemical model simulations with MAVEN/EUVM solar flux and the LMD GCM as inputs of the model. The global shape of the profile and the intensities are generally well reproduced. However, the peak altitude can sometimes be underestimated by the model and needs an adjustment of the CO2 density to reproduce the observations. We also compare the variations of the green line intensities over some individual UVIS limb tracking observations (observations of the atmosphere at a quasi-constant altitude) to model simulations and demonstrate a very good agreement. Finally, we show that the intensity and altitude of the lower emission peak are correlated with the solar Ly-α flux as expected from the theory of its production

Mars ultra-violet dayglow from NOMAD/UVIS

The UVIS (UV and Visible Spectrometer) channel of the NOMAD (Nadir and Occultation for MArs Discovery) spectrometer onboard the ExoMars Trace Gas Orbiter performs limb observations of the dayside of the Mars atmosphere in both the visible and the ultraviolet domains since April 2019. The recently discovered visible emissions of the oxygen green line (557.7 nm) and the oxygen red line doublet (630.0 and 636.4 nm) have already been investigated by Soret et al. (2022). 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 this study. 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 previous missions but it is the first time that both the 297.2 and 557.7 nm can be observed simultaneously by the same instrument. 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 CO Cameron bands, that have not been studied from the UVIS observations so far, are also presented. Finally, the CO2+ Fox-Duffendack-Barker (FDB) system, that has never 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. NOMAD/UVIS spectrometer is the first instrument that allows studying these UV emissions simultaneously that can, thus, be directly compared

Ultraviolet dayglow emissions and ratios in the Mars atmosphere

The 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-