Computer Science
Scientific paper
May 1991
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1991sdum.nasa...58w&link_type=abstract
In NASA. Ames Research Center, Sand and Dust on Mars p 58-59 (SEE N91-27057 18-91)
Computer Science
Diurnal Variations, Dust, Ground Wind, Mars (Planet), Mars Surface, Particle Motion, Sands, Solar Radiation, Stratification, Cooling, Friction, Heating, Low Speed, Planetary Boundary Layer, Pressure, Richardson Number, Samples, Shear Stress, Simulation, Surface Properties, Velocity Distribution, Wind Tunnels, Wind Velocity
Scientific paper
Diurnal changes in solar radiation on Mars set up a cycle of cooling and heating of the planetary boundary layer, this effect strongly influences the wind field. The stratification of the air layer is stable in early morning since the ground is cooler than the air above it. When the ground is heated and becomes warmer than the air its heat is transferred to the air above it. The heated parcels of air near the surface will, in effect, increase the near surface wind speed or increase the aeolian surface stress the wind has upon the surface when compared to an unheated or cooled surface. This means that for the same wind speed at a fixed height above the surface, ground-level shear stress will be greater for the heated surface than an unheated surface. Thus, it is possible to obtain saltation threshold conditions at lower mean wind speeds when the surface is heated. Even though the mean wind speed is less when the surface is heated, the surface shear stress required to initiate particle movement remains the same in both cases. To investigate this phenomenon, low-density surface dust aeolian threshold measurements have been made in the MARSWIT wind tunnel located at NASA Ames Research Center, Moffett Field, California. The first series of tests examined threshold values of the 100 micron sand material. At 13 mb surface pressure the unheated surface had a threshold friction speed of 2.93 m/s (and approximately corresponded to a velocity of 41.4 m/s at a height of 1 meter) while the heated surface equivalent bulk Richardson number of -0.02, yielded a threshold friction speed of 2.67 m/s (and approximately corresponded to a velocity of 38.0 m/s at a height of 1 meter). This change represents an 8.8 percent decrease in threshold conditions for the heated case. The values of velocities are well within the threshold range as observed by Arvidson et al., 1983. As the surface was heated the threshold decreased. At a value of bulk Richardson number equal to -0.02 the threshold friction speed and threshold wind speed appears to level-off to a constant value. This trend also was observed in the MARSWIT experiments involving the 11 micron sized-silt material.
Greeley Ronald
Leach Rodman N.
White Bruce R.
No associations
LandOfFree
Martian dust threshold measurements: Simulations under heated surface conditions does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.
If you have personal experience with Martian dust threshold measurements: Simulations under heated surface conditions, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Martian dust threshold measurements: Simulations under heated surface conditions will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-1040914