Field measurements demonstrate distinct initiation and cessation thresholds governing aeolian sediment transport flux

TL;DR

This study provides the first field-based evidence that aeolian sediment transport involves distinct fluid and impact thresholds, with the impact threshold primarily controlling average flux.

Contribution

It introduces field measurements that distinguish fluid and impact thresholds, improving understanding of sediment transport initiation and cessation.

Findings

Saltation activity is mainly governed by wind exceeding the fluid threshold when inactive.

Impact threshold becomes dominant as saltation activity increases.

Time-averaged flux is primarily controlled by the impact threshold.

Abstract

Wind-blown sand and dust models depend sensitively on the threshold wind stress. However, laboratory and numerical experiments suggest the coexistence of distinct "fluid" and "impact" thresholds for the initiation and cessation of aeolian saltation, respectively. Because aeolian transport models typically use only the fluid threshold, existence of a separate lower impact threshold complicates the prediction of wind-driven transport. Here, we derive the first field-based estimates of distinct fluid and impact thresholds from high-frequency saltation measurements at three field sites. Our measurements show that, when saltation is mostly inactive, its instantaneous occurrence is governed primarily by wind exceedance of the fluid threshold. As saltation activity increases, so too does the relative importance of the impact threshold, until it dominates under near-continuous transport conditions. Although both thresholds are thus important for high-frequency saltation prediction, we find that the time-averaged saltation flux is primarily governed by impact threshold.