Computer Science
Scientific paper
Dec 1992
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992msat.work...22b&link_type=abstract
In Lunar and Planetary Inst., Workshop on the Martian Surface and Atmosphere Through Time p 22 (SEE N92-28988 19-91)
Computer Science
Atmospheric Boundary Layer, Earth (Planet), Length, Mars (Planet), Surface Roughness, Terrain, Venus (Planet), Wind Effects, Wind Profiles, Alluvium, Arid Lands, Death Valley (Ca), Entrainment, Estimating, Fluid Flow, Friction, Lava, Mojave Desert (Ca), Nevada, Planetary Environments, Playas, Shear Stress
Scientific paper
The aerodynamic roughness length (z0) is the height at which a wind profile assumes a zero velocity. The lower part of the atmospheric boundary layer will be impeded by friction with the surface. An increase in surface roughness will also increase the shear stress required to initiate particle entrainment by the wind. Bagnold (1941) estimated z0 as being 1/30 of the mean particle size. In Nature, surface roughness is composed of nonerodible elements as well as sand-size erodible particles. To assess z0 values as a function of terrain, field experiments were conducted to obtain wind profiles monitored over natural surfaces at 15 sites in the Mojave Desert, Death Valley, and Nye County, Nevada. These sites span a variety of arid-land terrains, including smooth playas, alluvial fans, and lava flows; z0 values ranged from 0.0001 cm to 1 cm. These values were incorporated in a threshold model and a flux model to assess transport efficiency over such terrains in three planetary environments (Venus, Earth, and Mars), and for particle sizes ranging from 60-500 micron. Threshold and flux are a function of planetary environment, particle density and size (Dp), and z0, and the shear velocity of 1.2 x U*t (for Dp = 250 micron and z0 = 0.84). Results show that flux on Mars is approximately 14 g/(cm x s), on Earth it is approximately 3 g/(cm x s), and on Venus 0.5 g/(cm x s). Under all planetary environments, the results also show a dramatic decrease in the flux for particles greater than 200 microns when z0 increases above 0.0085 cm (corresponding to sites consisting of alluvium). When z0 approaches 0.03 cm (corresponding to a mantled pahoehoe lava), the flux diminishes.
Blumberg Dan G.
Greeley Ronald
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