Spectroscopic detection of low latitudes carbon dioxide clouds in the middle atmosphere of Mars

Details Spectroscopic detection of low latitudes carbon dioxide clouds in the middle atmosphere of Mars Spectroscopic detection of low latitudes carbon dioxide clouds in the middle atmosphere of Mars

Dec 2006

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006agufm.p14a..03m&link_type=abstract

American Geophysical Union, Fall Meeting 2006, abstract #P14A-03

Physics

0320 Cloud Physics And Chemistry, 0343 Planetary Atmospheres (5210, 5405, 5704), 5405 Atmospheres (0343, 1060)

Scientific paper

The formation of clouds resulting from the condensation of the main atmospheric component is a phenomenon peculiar to Mars. In spite of former observations reporting the likely presence of CO2 condensates lofted in the Martian atmosphere, no firm spectroscopic detection has ever been provided to date. Here, we report the existence of several regions located near the equator where a particular type of emission at 2.7 and 4.24 μm has been obtained by the visible/near-infrared mapping spectrometer OMEGA onboard Mars Express. This emission cannot be attributed to the previously discovered non-LTE fluorescent emission of gaseous CO22. OMEGA imaging capability indicates patchy areas of emission with strong spatial heterogeneities. Consideration of CO2 ice optical properties in this spectral range reveals the presence of major features which can result in brightness peaks for large enough particles (>100 nm). We have investigated this phenomenon by means of detailed spectroscopic and radiative transfer modelling. We conclude that the apparent emission is the likely result of photons resonantly scattered back to space by layers of carbon dioxide clouds. The fact that such clouds can be detected at the center of opaque absorption bands of gaseous CO2 requires clouds lofted above a certain altitude (>30 km) to reduce the optical path. Simultaneous observations by SPICAM allow to characterize CO2ice clouds in the ultraviolet. The analysis of cloud spectral dependence indicates particle size of the order of 400 nm.

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