soil transport by winds on Mars

Abstract

The eolian transport of surface material on the planet Mars is estimated from results of low-pressure wind tunnel testing and theoretical considerations. A semiempirical relation is developed that will estimate the total amount of surface material moving in eolian saltation, suspension, and surface traction. The estimated total mass movement of surface material per unit width time on the surface of Mars is q = 2.61p(V, -V,t)(V, + V,t)2/g (g/cm s), wherep is the density of the atmospheric gas, g is the acceleration due to gravity, and V, and V,t are the friction speed and saltation threshold friction speed, respectively. A flat surface composed of particles of nearly uniform size is assumed. A change in the mean particle size changes the threshold friction speed V,t. The path lengths of saltating particles and wavelengths of surface ripples can vary as much as a factor of 2 if the surface temperature varies from 150 to 250 K. The angles between particle paths and the horizontal surface are calculated to be lower on Mars than on earth, and particles travel much faster on Mars than on earth. The ratio of final particle velocity to threshold friction speed, VF/V,t, is found to be several times that of saltation on earth. l NTRODUCTION This paper presents three aspects of the movement of surface material by wind on Mars and assembles them to estimate transport rates. First, the governing equations of motion are presented and their numerical solutions. These are discussed with applications to Mars. Second, an analytical theory is presented from which one may estimate the surface flux. Last, results from low-pressure wind tunnel experiments are presented and are used to complete the semiempirical relation-

Aeolian sand transport: a wind tunnel model

“…Sand transport rate increases with an increase in wind velocity, but decreases with an increase in grain size. This, in a qualitative sense, agrees with Kawamura's (1951), Kind's (1976), and White's (1979) conclusions, but disagrees with Bagnold's (1941), Zingg's (1953), Hsu's (1971), Maegley's (1976, and Lettau and Lettau's (1978) results. The first attempt here is to relate transport rate to wind velocity at the centerline height of the wind tunnel.…”

“…The more turbulent airstream with greater Reynolds number produces greater lift force entraining sand particles (Bagnold, 1941). According to the field and wind tunnel studies by several pioneer workers (Bagnold, 1941;Greeley et al, 1974;White, 1979), the coefficient A decreases rapidly with particle friction Reynolds number when Re *t < 1, but becomes asymptotic when Re *t >1, with an ultimate value ranging between 0.1 and 0.118. Ascribing a constant value to A means the wind regime entraining particles is fully turbulent.…”

“…The effect of grain size on transport rate differs greatly between models. In some models (Zingg, 1953;Maegley, 1976;Lettau and Lettau, 1978), transport rate increases with an increase in grain size, while in some other models (Kawamura, 1951;Kind, 1976;White, 1979), transport rate decreases with an increase in grain size. In Hsu's (1971) model, the 0.325-mm sand has the least transport rate.…”

“…This type of equations have relatively sound theoretical support but a very severe limitation that they output meaningless sand transport when the shear velocity is less than the threshold. To overcome this drawback, the threshold shear velocity is included in the modified Bagnold-type equations (Kawamura, 1951;Owen, 1964;Iversen et al, 1976;Kind, 1976;Maegley, 1976;Lettau and Lettau, 1978;White, 1979). In fact, Bagnold's equation also has an implicit threshold term that makes the equation used only when the sand is moving.…”

Periodic saltation over hydrodynamically rough beds: aeolian to aquatic

“…The differences in saltation occur because of the difference in the mass density of the material of the grains relative to that of air and water and the differences in the kinematic viscosities of the two fluids. Saltation of grains of other mass densities in other atmospheres and other gravities is possible and has been described (Burr et al 2015, Greeley et al 1984, Iversen & White 1982, White 1979.…”