Modelling the Martian CO2 Ice Clouds

Constantino Listowski 1 Anni Määttänen 1 Franck Montmessin 1 Franck Lefèvre 1
1 IMPEC - LATMOS
LATMOS - Laboratoire Atmosphères, Milieux, Observations Spatiales
Abstract : Martian CO2 ice cloud formation represents a rare phenomenon in the Solar System: the condensation of the main component of the atmosphere. Moreover, on Mars, condensation occurs in a rarefied atmosphere (large Knudsen numbers, Kn) that limits the growth efficiency. These clouds form in the polar winter troposphere and in the mesosphere near the equator. CO2 ice cloud modeling has turned out to be challenging: recent efforts (e.g. [1]) fail in explaining typical small sizes (80 nm-130 nm) observed for mesospheric clouds [2]. Supercold pockets (T<< Tcond), which appear to be common in the mesosphere [3], might be exclusively responsible of the formation of such clouds, as a consequence of gravity waves propagating throughout the atmosphere [4]. In order to understand by modeling the effect CO2 clouds could have on the Martian climate, one needs to properly predict the crystal sizes, and so the growth rates involved. We will show that Earth microphysical crystal growth models, which deal with the condensation of trace gases, are misleading when transposed for CO2 cloud formation: they overestimate the growth rates at high saturation ratios. On the other hand, an approach based on the continuum regime (small Kn), corrected to account for the free molecular regime (high Kn) remains efficient. We present our new approach for modelling the growth of Martian CO2 cloud crystals, investigated with a 1D-microphysical model. [1] Colaprete, A., et al., (2008) PSS, 56, 150C [2] Montmessin, F., et al., (2006) Icarus, 183, 403-410 [3] Montmessin at al., (2011) mamo, 404-405 [4] Spiga, A., et al., (2012), GRL, 39, L02201 [5] Wood, S. E., (1999), Ph.D. thesis, UCLA [6] Young, J. B., J. Geophys. Res., 36, 294-2956, 1993
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Communication dans un congrès
44th Annual Meeting of the Division for Planetary Sciences of the American Astronomical Society, Oct 2012, Reno, United States
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Soumis le : mardi 6 novembre 2012 - 14:12:52
Dernière modification le : mardi 29 mai 2018 - 12:51:05

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Constantino Listowski, Anni Määttänen, Franck Montmessin, Franck Lefèvre. Modelling the Martian CO2 Ice Clouds. 44th Annual Meeting of the Division for Planetary Sciences of the American Astronomical Society, Oct 2012, Reno, United States. 〈hal-00748996〉

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