Intermittent Aeolian Saltation Over a Gobi Surface: Threshold, Saltation Layer Height, and High-Frequency Variability

Abstract

Gobi is a type of desert pavement in Asia over which aeolian saltation generates atmospheric dust. However, the high-frequency behavior of aeolian saltation over gobi is still poorly understood. In this study, coupled high-frequency observations of three-dimensional (3-D) wind speed (U) and saltation particle count rate in a vertical array of Sensit sensors were performed in a gobi region of Milan County, southern Xinjiang, China. The results revealed that aeolian saltation over a gobi surface exhibited an intermittent phenomenon, and the level of the intermittency was governed by the relative wind strength (s), which is consistent with that of sand surfaces. The threshold wind speed (Ut) decreased exponentially with increasing transport activity parameter (AP), and a prominent decrease in Ut was examined when the AP values reached 0.7; comparatively, for sand surfaces, a linearly declining trend occurred over the whole AP range of 0–1. The saltating particles over the gobi surface were distributed in layers of 0.08–0.30 m with an average value of 0.20 ± 0.04 m, which was significantly larger than that of sand surfaces. The relationship between the instantaneous sand transport rate (Q) and U over the gobi surface was also relatively poor and could be improved by lagging Q by 2 s. The mechanism for the collision between saltating particles and the gobi bed, which is rigid and complex in texture, was significantly different from that of the soft and deforming sand bed, causing the difference in aeolian saltation between gobi and sand surfaces.