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Communication Dans Un Congrès Année : 2021

The MY34 Global Dust Storm: Insights from data assimilation

Résumé

The ExoMars Trace Gas Orbiter (TGO), a collaborative project between the European Space Agency (ESA) and Roscosmos (Russia), has been taking observations from its 400km science orbit around Mars since late March 2018. Among its instruments, ACS/TIRVIM is a thermal infrared spectrometer with spectral range 1.7--17$\mu$m, whose main purpose is to continuously monitor the Martian environment in nadir in support of solar occultation measurements by ACS's near-infrared and mid-infrared channels. TIRVIM measures radiance spectra from which can be retrieved vertical profiles of atmospheric temperature, as well as surface temperatures and vertically-integrated amounts of dust and water ice, at various local times, latitudes and seasons. At UAE University, in collaboration with the Laboratoire de Météorologie Dynamique (LMD) and the ACS Science Team, we are studying Mars' atmosphere by assimilating data from TIRVIM into the LMD Mars Global Climate Model (LMD Mars GCM). The LMD Mars GCM is a detailed model of Mars' atmosphere that includes representations of the dust cycle, water cycle, boundary layer, subsurface, aerosols, upper atmosphere, and other parametrizations relevant to the Martian environment. We have assimilated data from TGO-ACS into the LMD Mars GCM using an assimilation scheme based on the Local Ensemble Transform Kalman Filter (LETKF), where we typically use 16 ensemble members and multiplicative inflation to adjust the background ensemble error covariance. This work focuses on atmospheric temperatures retrieved from nadir thermal emission spectra taken between 13 March 2018 (MY34 $L _{s} = 142.88$) and 15 July 2018 (MY34, $L _s = 211.43$). These have been calibrated and then retrieved using a line-by-line radiative transfer model. The observations cover various local times of day with full coverage in longitude every 7--10 days, over $\pm$75 degree latitude, with vertical coverage between 3--45 km altitude. A first for Mars data assimilation is the systematic coverage of all local times of day over a 55 Martian day cycle, which has not been possible hitherto, but which TGO's orbit was designed for. We shall present our analysis of the MY34 Global Dust Storm (GDS), which began in early June 2018. The GDS has a significant effect on the atmospheric state. In particular, we can retrieve the temperature response of the diurnal and semi-diurnal tides, and the response of the meridional circulation during the GDS, which cannot be measured directly but which can be revealed using data assimilation. Of particular interest are the differences between the assimilation and the free-running GCM, and the atmospheric state at local times of day that have not been observed prior to TGO.
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Dates et versions

insu-04503195 , version 1 (13-03-2024)

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Citer

Roland Young, Francois Forget, Alexander Trokhimovskiy, Nikolay Ignatiev, Ehouarn Millour, et al.. The MY34 Global Dust Storm: Insights from data assimilation. 43rd COSPAR Scientific Assembly, Jan 2021, Online, Unknown Region. pp.Abstract B4.1-0017-21 (oral), id.384. ⟨insu-04503195⟩
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