Mars water vapor vertical distributions from the troposphere to the mesosphere from NOMAD Solar Occultation for Martian Years 34 and 35
- 1Instituto de Astrofísica de Andalucía (IAA-CSIC), Granada, Spain (adrianbm@iaa.es)
- 2The University of Tokyo, Tokyo, Japan
- 3Royal Belgian Institute for Space Aeronomy, Belgium
- 4NASA Goddard Space Flight Center, USA
- 5American University, Washington DC, USA
- 6Open University, UK
- 7Istituto di Astrofisica e Planetologia, Italy
NOMAD [1] (Nadir and Occultation for MArs Discovery) is a multi-channel spectrometer onboard the ExoMars 2016 Trace Gas Orbiter (TGO), which began its observations in April 2018. The Solar Occultation (SO) channel has a spectral range coverage from 2.3 to 4.3 μm (2320 to 4350 cm-1), where numerous ro-vibrational bands of H2O are located. An Acousto-Optical Tunable Filter (AOTF) is used to select different spectral windows (with a typical width from 20 to 35 cm-1) corresponding to the desired diffraction orders to be used during an atmospheric scan. The SO channel has a sample rate of ∼1 s, that allows a vertical sampling of typically 1 km. In order to obtain as much information as possible from the Martian atmosphere, for this study we have analyzed data from diffraction orders 134 (3011-3035 cm-1), 136 (3056-3081 cm-1), 168 (3775-3805 cm-1) and 169 (3798-3828 cm-1), taken during different solar occultation scans since the beginning of the science operations phase of the TGO/ExoMars mission. This combination of diffraction orders allowed us to obtain an optimal mapping of the distribution of the water vapor at altitudes from ∼10 km up to about ∼100 km and in different atmospheric conditions, and hence, permitting the study of its spatial and seasonal variability.
The data presented here have been analyzed with pre-processing and cleaning tools developed entirely at the IAA (see companion contributions to this conference [2-4]), and then, inverted using a state-of-the-art retrieval scheme [5]. For the inversion, we have introduced a novel strategy of combining (when coincident in the same solar occultation) pairs of NOMAD orders (in contrast to a post-processing strategy), using orders 134 or 136 for the lower atmosphere, commonly below 60 km, and orders 168 or 169 for the upper atmosphere. This combination procedure allows us to exclude heavily saturated absorption lines present at low altitudes in orders 168-169, which contain strong absorption lines, permitting the exploitation of these orders for the analysis of the atmosphere up to 100 km. Here we present and discuss detailed maps showing the vertical distribution of the water vapor abundance of a subset of the solar occultations observed during the first two years of TGO/ExoMars. This research confirms some findings also obtained by other teams within the NOMAD consortium [6-8] and ACS instrument [9], showing that dust storms allow water vapor to reach higher altitudes in the atmosphere. This is important for the escape of atomic hydrogen [10] and therefore, for the long-term evolution of the Martian atmosphere. Detailed studies on the characterization of the Martian hygropause and saturation events are also presented.
Acknowledgments
The IAA/CSIC team acknowledges financial support from the State Agency for Research of the Spanish MCIU through the 'Center of Excellence Severo Ochoa' award for the Instituto de Astrofísica de Andalucía (SEV- 2017-0709) and funding by grant PGC2018-101836-B-100 (MCIU/AEI/FEDER, EU). ExoMars is a space mission of the European Space Agency (ESA) and Roscosmos. The NOMAD experiment is led by the Royal Belgian Institute for Space Aeronomy (IASB-BIRA), assisted by Co-PI teams from Spain (IAA-CSIC), Italy (INAF-IAPS), and the United Kingdom (Open University). US investigators were supported by the National Aeronautics and Space Administration.
References
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How to cite: Brines, A., Lopez Valverde, M. Á., Stolzenbach, A., Modak, A., Funke, B., Gonzalez Galindo, F., Lopez Moreno, J. J., Aoki, S., Vandaele, A. C., Daerden, F., Thomas, I., Erwin, J., Trompet, L., Ristic, B., Villanueva, G. L., Liuzzi, G., Patel, M., and Bellucci, G.: Mars water vapor vertical distributions from the troposphere to the mesosphere from NOMAD Solar Occultation for Martian Years 34 and 35, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-504, https://doi.org/10.5194/epsc2022-504, 2022.
