High-altitude CO2 clouds on Mars: A view from MEx observations, the LMD MGCM, and convective potential calculations

Abstract : We will summarize 3.5 Martian years (Mars Years 27-30) of high-altitude CO2 cloud data from MEx/OMEGA and selected results from Mex/HRSC. The 3-year dataset shows that the equatorial cloud activity is centered around the northern summer solstice with a pause at the aphelion, and that their appearance is limited in latitude and longitude. HRSC-measured altitudes and cloud speeds provide a rare dataset for comparison with GCMs. A comparison with the LMD Mars Global Climate Model shows a good agreement between the model-predicted winds and those observed by the HRSC. The LMD-MGCM predicts a strong diurnal variation of temperature at the cloud observation altitudes due to the propagation of the diurnal thermal tide. The coldest temperatures in the near-equator cloud altitude range (60-85 km) are observed towards the end of the afternoon, whereas the warmest temperatures are found in the early morning hours. Most of the observed clouds are cirrus-type, filamented clouds, but some OMEGA-observed clouds exhibit round, clumpy structures that have been suggested to be of convective origin. We asses the plausibility of the hypothesis of mesospheric convection in light of observations and theoretical Convective Available Potential Energy calculations. Estimates of convective potential and vertical velocities based on observed cloud properties suggest that the convective clouds could most likely be clusters of smaller scale convective updrafts. SPICAM stellar occultations have revealed large supersaturations at high altitudes: to attain the estimated values of CAPE and vertical velocity, most probably only moderate deviations from saturation are required. Based on nucleation modeling, such deviations may imply cloud formation via heterogeneous nucleation onto small condensation nuclei.
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Soumis le : samedi 19 novembre 2011 - 15:53:09
Dernière modification le : mercredi 28 novembre 2018 - 15:06:01



Anni Määttänen, Franck Montmessin, Brigitte Gondet, H. Hoffmann, F. Scholten, et al.. High-altitude CO2 clouds on Mars: A view from MEx observations, the LMD MGCM, and convective potential calculations. Bulletin of the American Astronomical Society, 2010, 42, pp.1047. 〈hal-00642904〉



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