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G. Tobie, F. Lott, F. Forget (Laboratoire de Meteorologie Dynamique, Paris, France)
In 1998, the Mars Orbiter Laser Altimeter experiment revealed the presence of thick clouds above the north polar cap during the polar night, thought to be composed of CO2 ice. Of particular interest are clouds with sloping tops that are assumed to mark the propagating phase fronts of gravity waves [1] [2].
In order to model induced wave CO2 ice clouds formation, we have adapted a two-dimensional linear anelastic terrestrial mountain waves model [3] to the winter polar martian atmosphere. The various aspects of the CO2 ice physics (condensation, microphysics, ice transport) have been included. The background polar atmosphere mean state was deduced from the LMD martian General Circulation Model [4]. According to the GCM, we found that the winter polar atmosphere exhibits a particular behaviour of temperature and wind profiles at the lowest altitude, able to induce atypical trapped lee waves features.
Within this context, the model is able to reproduce the main characteristic of the observations. It suggests that the observed clouds are not consequence of a resonant trapped lee wave but of multiple wave number interferences. As the polar atmosphere don't select preferentially a gravity wave mode, the simulated clouds features strongly depend on topography. We have envisaged differents microphysics scenarios and investigated simulated clouds detectability by MOLA
[1] Zuber et al. Science 282, 2053-2060, 1998.
[2] Pettengill and Ford, Geophys.Res.Lett 27, 609-612, 2000.
[3] Lott, Tellus 50A, 12-25 1998.
[4] Forget et al. J.Geophys.Res 104, 24,155-24,176, 1999.
The author(s) of this abstract have provided an email address for comments about the abstract: tobie@lmd.jussieu.fr