DPS 34th Meeting, October 2002
Session 5. Mars Atmosphere I
Oral, Chair: D.L. Huestis, Monday, October 7, 2002, 11:30am-1:00pm, Room M

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[5.09] Numerical Simulations of Martian Fog Formation in the Low Latitudes

A. Inada (Max Planck Institut fuer Aeronomie)

The formation of Martian surface fog is simulated by a one-dimensional model including the micro-physical processes of heterogeneous nucleation, condensation, and sublimation. The model includes diurnal cycle of water vapor in the 1 km surface layer which is spatially resolved. The results show that the column density of water ice in fog strongly depends on the water vapor density near the surface. If the mixing ratio of water vapor is 300 ppm near the surface, the simulations show that a thin fog layer appears with a maximum column density of 0.145 precipitable microns. If the mixing ratio is 600 ppm, the value measured by the Mars Pathfinder, the column density of water ice reaches 0.75 precipitable microns. It is also found that if the boundary layer is strongly turbulent the total amount of ice formed is small, since the ice particles are transported to the unsaturated higher atmospheric layers and sublimate there. Fog particles, which are large enough to precipitate to the lower atmosphere play a significant role in determining the altitude distribution of water vapor. It is noteworthy that the size distribution of all of the aerosols has two peaks once fog appears. This is because nucleation on large dust particles is so much faster than on the small ones, that the small dust particles are hardly coated by ice. The simulations assume an initial dust distribution with effective radius of 1.6 microns. Once fog forms this peak remains and is populated with particles with little water ice. A secondary peak is formed at about 10 microns corresponding to particles which are mostly water ice.

This research was carried out under the partial support of JSPS Postdoctoral Fellowships for Research Abroad.

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Bulletin of the American Astronomical Society, 34, #3< br> © 2002. The American Astronomical Soceity.