Icarus (2019), https://doi.org/10.1029/2019GL084354
L. Neary, F. Daerden, S. Aoki, J. Whiteway, R. T. Clancy, M. Smith, S. Viscardy, J. T. Erwin, I. R. Thomas, G. Villanueva, G. Liuzzi, M. Crismani, M. Wolff, S. R. Lewis, J. A. Holmes, M. R. Patel, M. Giuranna, C. Depiesse, A. Piccialli, S. Robert, L. Trompet, Y. Willame, B. Ristic, A. C. Vandaele
The Nadir and Occultation for MArs Discovery (NOMAD) instrument on board ExoMars Trace Gas Orbiter (TGO) measured a large increase in water vapor at altitudes in the range of 40-100 km during the 2018 global dust storm on Mars. Using a three-dimensional general circulation model, we examine the mechanism responsible for the enhancement of water vapor in the upper atmosphere. Experiments with different prescribed vertical profiles of dust show that when more dust is present higher in the atmosphere the temperature increases and the amount of water ascending over the tropics is not limited by saturation until reaching heights of 70-100 km. The warmer temperatures allow more water to ascend to the mesosphere. Photochemical simulations show a strong increase in high-altitude atomic hydrogen following the high-altitude water vapor increase by a few days.
Ann Carine Vandaele, Oleg Korablev, Frank Daerden, Shohei Aoki, Ian R. Thomas, Francesca Altieri, Miguel López-Valverde, Geronimo Villanueva, Giuliano Liuzzi, Michael D. Smith, Justin T. Erwin, Loïc Trompet, Anna A. Fedorova, Franck Montmessin, Alexander Trokhimovskiy, Denis A. Belyaev, Nikolay I. Ignatiev, Mikhail Luginin, Kevin S. Olsen, Lucio Baggio, Juan Alday, Jean-Loup Bertaux, Daria Betsis, David Bolsée, R. Todd Clancy, Edward Cloutis, Cédric Depiesse, Bernd Funke, Maia Garcia-Comas, Jean-Claude Gérard, Marco Giuranna, Francisco Gonzalez-Galindo, Alexey V. Grigoriev, Yuriy S. Ivanov, Jacek Kaminski, Ozgur Karatekin, Franck Lefèvre, Stephen Lewis, Manuel López-Puertas, Arnaud Mahieux, Igor Maslov, Jon Mason, Michael J. Mumma, Lori Neary, Eddy Neefs, Andrey Patrakeev, Dmitry Patsaev, Bojan Ristic, Séverine Robert, Frédéric Schmidt, Alexey Shakun, Nicholas A. Teanby, Sébastien Viscardy, Yannick Willame, James Whiteway, Valérie Wilquet, Michael J. Wolff, Giancarlo Bellucci, Manish R. Patel, Jose-Juan López-Moreno, François Forget, Colin F. Wilson, Håkan Svedhem, Jorge L. Vago, Daniel Rodionov, NOMAD Science Team & ACS Science Team
Global dust storms on Mars are rare but can affect the Martian atmosphere for several months. They can cause changes in atmospheric dynamics and inflation of the atmosphere, primarily owing to solar heating of the dust. In turn, changes in atmospheric dynamics can affect the distribution of atmospheric water vapour, with potential implications for the atmospheric photochemistry and climate on Mars. Recent observations of the water vapour abundance in the Martian atmosphere during dust storm conditions revealed a high-altitude increase in atmospheric water vapour that was more pronounced at high northern latitudes, as well as a decrease in the water column at low latitudes. Here we present concurrent, high-resolution measurements of dust, water and semiheavy water (HDO) at the onset of a global dust storm, obtained by the NOMAD and ACS instruments onboard the ExoMars Trace Gas Orbiter. We report the vertical distribution of the HDO/H2O ratio (D/H) from the planetary boundary layer up to an altitude of 80 kilometres. Our findings suggest that before the onset of the dust storm, HDO abundances were reduced to levels below detectability at altitudes above 40 kilometres. This decrease in HDO coincided with the presence of water-ice clouds. During the storm, an increase in the abundance of H2O and HDO was observed at altitudes between 40 and 80 kilometres. We propose that these increased abundances may be the result of warmer temperatures during the dust storm causing stronger atmospheric circulation and preventing ice cloud formation, which may confine water vapour to lower altitudes through gravitational fall and subsequent sublimation of ice crystals. The observed changes in H2O and HDO abundance occurred within a few days during the development of the dust storm, suggesting a fast impact of dust storms on the Martian atmosphere.
Liuzzi, G.; Villanueva, G.L.; Mumma, M.J.; Smith, M.D.; Daerden, F.; Ristic, B.; Thomas, I.; Vandaele, A.C.; Patel, M.R.; Lopez-Moreno, J.-J.; Bellucci, G.
The Nadir and Occultation for MArs Discovery instrument (NOMAD), onboard the ExoMars Trace Gas Orbiter (TGO) spacecraft was conceived to observe Mars in solar occultation, nadir, and limb geometries, and will be able to produce an outstanding amount of diverse data, mostly focused on properties of the atmosphere. The infrared channels of the instrument operate by combining an echelle grating spectrometer with an Acousto-Optical Tunable Filter (AOTF). Using in-flight data, we characterized the instrument performance and parameterized its calibration. In particular: an accurate frequency calibration was achieved, together with its variability due to thermal effects on the grating. The AOTF properties and transfer function were also quantified, and we developed and tested a realistic method to compute the spectral continuum transmitted through the coupled grating and AOTF system. The calibration results enabled unprecedented insights into the important problem of the sensitivity of NOMAD to methane abundances in the atmosphere. We also deeply characterized its performance under realistic conditions of varying aerosol abundances, diverse albedos and changing illumination conditions as foreseen over the nominal mission. The results show that, in low aerosol conditions, NOMAD single spectrum, 1σ sensitivity to CH4 is around 0.33 ppbv at 20 km of altitude when performing solar occultations, and better than 1 ppbv below 30 km. In dusty conditions, we show that the sensitivity drops to 0 below 10 km. In Nadir geometry, results demonstrate that NOMAD will be able to produce seasonal maps of CH4 with a sensitivity around 5 ppbv over most of planet's surface with spatial integration over 5 × 5° bins. Results show also that such numbers can be improved by a factor of ~10 to ~30 by data binning. Overall, our results quantify NOMAD's capability to address the variable aspects of Martian climate.
Oleg Korablev, Ann Carine Vandaele, Franck Montmessin, Anna A. Fedorova, Alexander Trokhimovskiy, François Forget, Franck Lefèvre, Frank Daerden, Ian R. Thomas, Loïc Trompet, Justin T. Erwin, Shohei Aoki, Séverine Robert, Lori Neary, Sébastien Viscardy, Alexey V. Grigoriev, Nikolay I. Ignatiev, Alexey Shakun, Andrey Patrakeev, Denis A. Belyaev, Jean-Loup Bertaux, Kevin S. Olsen, Lucio Baggio, Juan Alday, Yuriy S. Ivanov, Bojan Ristic, Jon Mason, Yannick Willame, Cédric Depiesse, Laszlo Hetey, Sophie Berkenbosch, Roland Clairquin, Claudio Queirolo, Bram Beeckman, Eddy Neefs, Manish R. Patel, Giancarlo Bellucci, Jose-Juan López-Moreno, Colin F. Wilson, Giuseppe Etiope, Lev Zelenyi, Håkan Svedhem, Jorge L. Vago & The ACS and NOMAD Science Teams
The detection of methane on Mars has been interpreted as indicating that geochemical or biotic activities could persist on Mars today. A number of different measurements of methane show evidence of transient, locally elevated methane concentrations and seasonal variations in background methane concentrations. These measurements, however, are difficult to reconcile with our current understanding of the chemistry and physics of the Martian atmosphere, which—given methane’s lifetime of several centuries—predicts an even, well mixed distribution of methane. Here we report highly sensitive measurements of the atmosphere of Mars in an attempt to detect methane, using the ACS and NOMAD instruments onboard the ESA-Roscosmos ExoMars Trace Gas Orbiter from April to August 2018. We did not detect any methane over a range of latitudes in both hemispheres, obtaining an upper limit for methane of about 0.05 parts per billion by volume, which is 10 to 100 times lower than previously reported positive detections. We suggest that reconciliation between the present findings and the background methane concentrations found in the Gale crater would require an unknown process that can rapidly remove or sequester methane from the lower atmosphere before it spreads globally.
Vandaele, A.C.; Lopez-Moreno, J.-J.; Patel, M.R.; Bellucci, G.; Daerden, F.; Ristic, B.; Robert, S.; Thomas, I.R.; Wilquet, V.; Allen, M.; Alonso-Rodrigo, G.; Altieri, F.; Aoki, S.; Bolsée, D.; Clancy, T.; Cloutis, E.; Depiesse, C.; Drummond, R.; Fedorova, A.; Formisano, V.; Funke, B.; González-Galindo, F.; Geminale, A.; Gérard, J.-C.; Giuranna, M.; Hetey, L.; Ignatiev, N.; Kaminski, J.; Karatekin, O.; Kasaba, Y.; Leese, M.; Lefèvre, F.; Lewis, S.R.; López-Puertas, M.; López-Valverde, M.; Mahieux, A.; Mason, J.; McConnell, J.; Mumma, M.; Neary, L.; Neefs, E.; Renotte, E.; Rodriguez-Gomez, J.; Sindoni, G.; Smith, M.; Stiepen, A.; Trokhimovsky, A.; Vander Auwera, J.; Villanueva, G.; Viscardy, S.; Whiteway, J.; Willame, Y.; Wolff, M.; the NOMAD Team
The NOMAD (“Nadir and Occultation for MArs Discovery”) spectrometer suite on board the ExoMars Trace Gas Orbiter (TGO) has been designed to investigate the composition of Mars’ atmosphere, with a particular focus on trace gases, clouds and dust. The detection sensitivity for trace gases is considerably improved compared to previous Mars missions, compliant with the science objectives of the TGO mission. This will allow for a major leap in our knowledge and understanding of the Martian atmospheric composition and the related physical and chemical processes. The instrument is a combination of three spectrometers, covering a spectral range from the UV to the mid-IR, and can perform solar occultation, nadir and limb observations. In this paper, we present the science objectives of the instrument and explain the technical principles of the three spectrometers. We also discuss the expected performance of the instrument in terms of spatial and temporal coverage and detection sensitivity.
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