Showing papers by "James D. Iversen published in 2003"
TL;DR: An apparatus has been fabricated to simulate terrestrial and Martian dust devils on both Earth and Mars as mentioned in this paper, and the results indicated that the wind speeds required for the entrainment of grains approx 2 microns in diameter (i.e., Martian dust sizes) are about half those required for entrainments by boundary layer winds on both earth and Mars.
Abstract: An apparatus has been fabricated to simulate terrestrial and Martian dust devils Comparisons of surface pressure profiles through the vortex core generated in the apparatus with both those in natural dust devils on Earth and those inferred for Mars are similar and are consistent with theoretical Rankine vortex models Experiments to determine particle threshold under Earth ambient atmospheric pressures show that sand (particles > 60 micron in diameter) threshold is analogous to normal boundary-layer shear, in which the rotating winds of the vortex generate surface shear and hence lift Lower-pressure experiments down to approx 65 mbar follow this trend for sand-sized particles However, smaller particles (ie, dust) and all particles at very low pressures (w 10-60 mbar) appear to be subjected to an additional lift function interpreted to result from the strong decrease in atmospheric pressure centered beneath the vortex core Initial results suggest that the wind speeds required for the entrainment of grains approx 2 microns in diameter (ie, Martian dust sizes) are about half those required for entrainment by boundary layer winds on both Earth and Mars
160 citations
TL;DR: In this paper, surface friction velocities (u*) and aerodynamic roughness heights (z0) at the base of 10 dust devils were determined using in-situ field measurements, and they appeared to be a linear function of the peak wind speed measured at ∼2 m height within the dust devil.
Abstract: [1] Using in-situ field measurements, we determined surface friction velocities (u*) and aerodynamic roughness heights (z0) at the base of 10 dust devils. z0 values agree closely with previous studies in this region and range from 0.1 to 1.0 cm. The peak u* coincide with the largest wind speed measurements within the dust devil and range from 0.9 to 2.4 ms−1. Surface friction velocities are sufficient to lift all types of windblown material from dust to pebble sized particles. Peak u* values for dust devils appear to be a linear function of the peak wind speed measured at ∼2 m height within the dust devil. This provides a simple approximation for estimating surface shear stress for dust devils.
42 citations