Seasonal Variations of Martian Clouds and Volatiles

Details Seasonal Variations of Martian Clouds and Volatiles Seasonal Variations of Martian Clouds and Volatiles

Sep 1999

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999dps....31.4903k&link_type=abstract

American Astronomical Society, DPS meeting #31, #49.03

Astronomy and Astrophysics

Astronomy

Scientific paper

Using the 256x256 InSb array NSFCAM at the NASA infrared Telescope Facility we have gathered near-infrared (NIR) multi-spectral image sets of Mars over the last three oppositions. We have been working on a long term-monitoring of the Martian volatiles and now have data enough to begin making seasonal comparisons. The opposition of 1995 happened during Martian northern spring (L_S = 45\arcdeg\ - 71\arcdeg) and the opposition of 1999 happened during Martian northern summer (L_S = 90\arcdeg\ - 129\arcdeg). We present here our analyses and comparisons of the cloud coverage and compositions at these two times. In our previous studies we developed band-ratio techniques which allow us to map the spectral signatures of both H_2O and CO_2 frosts and to distinguish between them and found evidence for clouds of CO_2 ices at the southern (winter) pole. For this paper we apply those same techniques to our newest data. We find that at L_S = 54\arcdeg\ the northern pole is still covered by a polar hood cloud with some significant amount of CO_2 ices still present in the polar cap. By L_S = 106\arcdeg\ there is only a small H_2O ice signature with no evidence of polar clouds. The thick tropical clouds of the Martian spring have also greatly diminished in the summer, although there is still a strong cloud signature at the limbs indicating that there is significant overnight cloud formation. Of interest is the lack of any strong CO_2 ice signatures during the northern spring/southern fall except for the ground ices still at the northern polar cap. By L_S = 129\arcdeg\ in the most extreme visible southern latitudes we see evidence of CO_2 ice clouds indicating the much colder winter climate of the southern hemisphere. These results, once calibrated to absolute flux units, will be used to calcualte H_2O and CO_2 ice amounts in an effort to help understand the volatile cycles and total water budget of Mars.

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