Analysis of the mass flux profiles of an aeolian saltating cloud

Abstract

Aeolian researchers have recognized the importance of measuring the height profile of aeolian saltating flux and devoted a lot of effort to reliable measurement. In this paper, the height profiles of aeolian saltation flux are reconstructed on the basis of the profiles of mean particle velocity and relative particle concentration obtained by particle image velocimetry, a nonintrusive technique, in a wind tunnel. The results suggest that the mean particle velocity increases with an increase in wind velocity and height but decreases with an increase in particle size. The height profile of mean particle velocity can be expressed by a power function, essentially in agreement with previous studies. Particle concentration decays exponentially with the square root of height rather than height itself as proposed in most previous studies. Mass flux profiles are derived by multiplying the mean particle velocity and concentration profiles. The reconstructed mass flux profiles are characterized by three sections. In the near-surface layer, mass flux increases with height. In the upper layer, mass flux decays exponentially with height. Between the near-surface and upper layers is a peak flux zone whose height above the surface increases with an increase in wind velocity but decreases with an increase in particle size. The reconstructed mass profiles are essentially in reasonably good agreement with those measured by a segmented sand sampler in a wind tunnel. Two significant parameters, average saltation height and relative decay factor, are proposed to characterize variation with height of aeolian saltating flux. They are well correlated and imply that saltating particles can reach higher levels as wind velocity increases and particle size decreases and that mass flux decays more rapidly as wind velocity decreases and particle size increases. Copyright 2006 by the American Geophysical Union.