Observations of the Polar Night Clouds on Mars with the Mars Orbiter Laser Altimeter (MOLA)

Details Observations of the Polar Night Clouds on Mars with the Mars Orbiter Laser Altimeter (MOLA) Observations of the Polar Night Clouds on Mars with the Mars Orbiter Laser Altimeter (MOLA)

Aug 2000

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2000mpse.conf...83i&link_type=abstract

International Conference on Mars Polar Science and Exploration, p. 83

Physics

Mars Atmosphere, Mars Environment, Mars Surface, Mars (Planet), Carbon Dioxide, Polar Caps, Polar Regions, Models, Climate, Clouds (Meteorology), Ice, Thermal Mapping

Scientific paper

Condensation of CO2 at the winter poles is a very important process in the current climate of Mars. Almost 25% of the Martian atmosphere is recycled through the polar ice caps every year. The condensed form of CO2 have never been observed or quantified in any significant detail. The Mars Orbiter Laser Altimeter (MOLA) is a very sensitive instrument and was able to detect faint returns coming from the clouds, forming over the polar regions when they were shrouded in winter darkness. The clouds are probably composed of CO2 ice, which formed in very cold polar winter temperatures. CO2 ice clouds were first suggested by Gierasch and Goody. A recent review by Forget discusses recent advances in modeling CO2 condensation rates during the polar night. A direct observation of CO2 clouds was made by the Mariner 6 and 7 infrared spectrometers; three bright limb crossings yielded spectra with a spike at 4.26 micrometers which was attributed to reflection in the strong v3 band from solid CO2 at approx. 25 km altitude. However, the range of occurrence of CO2 clouds was highly uncertain. The Viking Infrared Thermal Mapper (IRTM) instruments found areas in the winter polar regions with anomalously low brightness temperatures at 20 micrometer wavelength, some below 135K. The location and brightness temperatures of these areas sometimes varied on the scales of days, suggesting complex physical processes. In this presentation we will discuss continuing observations of the polar night clouds during the second North Polar Winter with the MOLA instrument. We will describe seasonal, spatial, and elevation distributions of the polar clouds and cloud opacities in the North and South Polar regions of Mars. We will also present some correlations between MOLA cloud heights and MGS Thermal Emission Spectrometer (TES) brightness temperature observations. Additional information is contained in the original extended abstract.

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