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Science 3 July 2009:
Vol. 325. no. 5936, pp. 68 - 70
DOI: 10.1126/science.1172344
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Reports

Mars Water-Ice Clouds and Precipitation

J. A. Whiteway,1,* L. Komguem,1 C. Dickinson,1 C. Cook,1 M. Illnicki,1 J. Seabrook,1 V. Popovici,1 T. J. Duck,2 R. Davy,1 P. A. Taylor,1 J. Pathak,1 D. Fisher,3 A. I. Carswell,4 M. Daly,5 V. Hipkin,6 A. P. Zent,7 M. H. Hecht,8 S. E. Wood,9 L. K. Tamppari,8 N. Renno,10 J. E. Moores,11 M. T. Lemmon,12 F. Daerden,13 P. H. Smith11

The light detection and ranging instrument on the Phoenix mission observed water-ice clouds in the atmosphere of Mars that were similar to cirrus clouds on Earth. Fall streaks in the cloud structure traced the precipitation of ice crystals toward the ground. Measurements of atmospheric dust indicated that the planetary boundary layer (PBL) on Mars was well mixed, up to heights of around 4 kilometers, by the summer daytime turbulence and convection. The water-ice clouds were detected at the top of the PBL and near the ground each night in late summer after the air temperature started decreasing. The interpretation is that water vapor mixed upward by daytime turbulence and convection forms ice crystal clouds at night that precipitate back toward the surface.

1 Department of Earth and Space Science and Engineering, York University, Toronto, Ontario, Canada.
2 Department of Physics and Atmospheric Science, Dalhousie University, Halifax, Nova Scotia.
3 National Glaciology Group, Geological Survey of Canada, Natural Resources Canada, Ottawa, Ontario, Canada.
4 Optech, Vaughan, Ontario, Canada.
5 MacDonald, Dettwiler and Associates (MDA), Brampton, Ontario, Canada.
6 Canadian Space Agency (CSA), St-Hubert, Quebec, Canada.
7 NASA Ames Research Center, Moffett Field, CA, USA.
8 Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA.
9 Department of Earth and Space Sciences, University of Washington, Seattle, WA, USA.
10 Department of Atmospheric, Oceanic and Space Sciences, University of Michigan, Ann Arbor, MI, USA.
11 Department of Planetary Sciences, University of Arizona, Tucson, AZ, USA.
12 Department of Atmospheric Sciences, Texas A&M University, College Station, TX, USA.
13 Belgian Institute for Space Aeronomy (BIRA-IASB), Brussels, Belgium.

* To whom correspondence should be addressed. E-mail: whiteway{at}yorku.ca

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THIS ARTICLE HAS BEEN CITED BY OTHER ARTICLES:
H2O at the Phoenix Landing Site.
P. H. Smith, L. K. Tamppari, R. E. Arvidson, D. Bass, D. Blaney, W. V. Boynton, A. Carswell, D. C. Catling, B. C. Clark, T. Duck, et al. (2009)
Science 325, 58-61
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