干旱区生态环境知识资源中心

Field experiments on boundary layer winds and sand transport in the Victoria Valley, Antarctica have provided information on the spatial and temporal variability of sand transport across coarse sand surfaces covered with isolated roughness elements (rock clusters). Five sand transport events, with a duration ranging between 9.6 and 22 h, were studied. Sand transport threshold velocity was determined using the time faction equivalence method and varied between 0.30 and 0.35 m s(-1). Mean rates of sand transport ranged from 0.008 to 0.072 (u*, cm s(-1). Sand transport was variably intermittent, with continuous saltation (intermittency (gamma) = 1) occurring from 11% to as much as 31% of the time. For all events, there is a close temporal correspondence between intermittency values, shear velocity (u*, m s(-1)) and the ratio u*/u*(tau) (u*tau is threshold shear velocity), sand flux, and sand transport intensity as measured by piezoelectric saltation sensors. Although the roughness density of this site is low, partitioning of shear stress between the rock clusters and the intervening sand surface is important to the spatial pattern of sand transport and acts to increase the mean threshold wind shear velocity or shear stress for sediment transport by approximately 1.2 times compared to a bare sand surface. The effective local threshold wind shear velocity, however, varies by up to 6 times from the smoother sand areas to the most protected areas of the rock clusters. As a result, continuous and widespread sand transport will only occur at this site when the overall wind shear velocity exceeds 0.58 m s(-1) (1.6 x u*(t) minimum).