First detection of Mars atmospheric hydroxyl: CRISM Near-IR measurement versus LMD GCM simulation of OH Meinel band emission in the Mars polar winter atmosphere

Abstract : Visible and near-IR Meinel band emissions originate from excited OH in the terrestrial upper atmosphere (Meinel, 1950), and have recently been detected in the Venus nightside upper mesosphere (Piccioni et al., 2008). Meinel band observations support key studies of transport and photochemistry in both of these atmospheres. In the case of Mars, OH regulates the basic stability of the CO2 atmosphere to photolytic decomposition (Parkinson and Hunten, 1972 to CO and O2, e.g.), and yet has never been measured. We present the first detection of Mars atmospheric OH, associated with CRISM near-IR spectral limb observations of polar night Meinel band emissions centered at 1.45 and 2.9 μμm. Meinel band (1-0), (2-1), and (2-0) average limb intensities of 990±±280, 1060±±480, and 200±±100 KiloRayleighs (kR), respectively, are determined for 70-90 NS polar winter latitudes over altitudes of 40-56 km. Additional OH bands, such as (3-2), (3-1), and (4-2), present ⩽⩽1σσ measurements. Uncertainty in the (4-2) band emission rate contributes to increased uncertainty in the determination of the (O21△g)(O21△g) (0-0)/(0-1) band emission ratio (A00/A01=A00/A01=View the MathML source47-12+26). An average profile retrieval for Mars OH polar nightglow indicates 45-55 km altitude levels for volume emission rates (VER) of 0.4 (2-0) to 2 (1-0, 2-1) x104 photons/(cm3sec). Similar to polar night (O21△g)(O21△g) emission (e.g. Clancy et al., 2012), Meinel OH band emission is supported by upper level, winter poleward transport of O and H in the deep Hadley solsticial circulations of Mars. The retrieved OH emission rates are compared to polar winter OH nightglow simulated by the LMD (Laboratoire de Météorologie Dynamique) photochemical GCM (global climate model), employing detailed photochemistry (e.g. Lefèvre et al., 2004) and energy transfer processes (excitation and quenching) developed for Mars Meinel OH band nightglow by Muñoz et al. (2005). Modeled versus observed OH emission behavior agrees within measurement uncertainties with the assumptions of a Bates-Nicolet (H+O3) source for excited OH production, and 'collisional-cascade' quenching of the OH vibrational population by CO2. 'Sudden-death' quenching of excited OH by CO2 leads to 100x less OH emission than observed. The combined agreement between LMD GCM simulated and CRISM observed (O21△g)(O21△g) and Meinel OH polar nightglow behaviors represents a significant demonstration of the LMD model capability to couple odd oxygen and hydrogen photochemistry and transport by the Mars global circulation in a realistic fashion.
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Soumis le : mardi 18 juin 2013 - 18:33:20
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R. Todd Clancy, Brad J. Sandor, Antonio García-Muñoz, Franck Lefèvre, Michael D. Smith, et al.. First detection of Mars atmospheric hydroxyl: CRISM Near-IR measurement versus LMD GCM simulation of OH Meinel band emission in the Mars polar winter atmosphere. Icarus, Elsevier, 2013, 226 (1), pp.272-281. 〈10.1016/j.icarus.2013.05.035〉. 〈hal-00835502〉



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