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J. L. Benson, B. P. Bonev, P. B. James, K. J. Shan (Ritter Astrophys. Res. Center, Dept. of Phys. & Astr., Univ. of Toledo), B. A. Cantor, M. A. Caplinger (Malin Space Science Systems)
The Mars Global Surveyor Mars Orbiter Camera was used to obtain global maps of the Martian surface with equatorial resolution of 7.5 km/pixel in two wavelength ranges: blue (400-450 nm) and red (575-625 nm). The maps used were acquired between March 15, 1999 (Ls = 110º) and July 31, 2001 (Ls = 205º), corresponding to approximately one and a quarter martian years. Using the global maps, cloud area (in km2) has been measured daily for water ice clouds topographically corresponding to Olympus Mons, Ascraeus Mons, Pavonis Mons, Arsia Mons, Alba Patera, the western Valles Marineris canyon system, and for other small surface features in the region. Seasonal trends in cloud activity have been established for each of the five Tharsis volcanoes. Olympus, Ascraeus, and Pavonis Mons show cloud activity from about Ls = 0º-220º with a peak in cloud area near Ls = 100º. One of our most interesting observational results is that Alba Patera shows a double peaked feature in the cloud area with peaks at Ls = 60º and 140º and a minimum near Ls = 100º. Arsia Mons shows nearly continuous cloud activity. A quasi-periodicity of 2.10-2.40 sols has been found in all five areas of the Tharsis region examined. It is most likely the combined result of the diurnal cloud variability during the afternoon hours and the motion of the spacecraft’s orbit. In addition, optical depth has been measured for 154 of the observed clouds. In general, the optical depth of clouds in the first martian year of our observations is smaller than that of the second year, except for Alba Patera, where the optical depths are similar. This work was supported by a Mars Participation Scientist grant and by a MGS Team Science Data Analysis grant, both from Jet Propulsion Laboratory.
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Bulletin of the American Astronomical Society, 34, #3< br> © 2002. The American Astronomical Soceity.