Size-independent susceptibility to transport in aeolian saltation

TL;DR

This study demonstrates that in natural aeolian saltation, different sand sizes share a common threshold for saltation, challenging previous models that treated each size independently and suggesting a simplified, more accurate modeling approach.

Contribution

The paper provides empirical evidence that all sand sizes in natural saltation share a single susceptibility threshold, refuting the assumption of size-selective saltation in mixed beds.

Findings

All sand sizes exhibit equal susceptibility to saltation at a common threshold.

Common models assuming size-selective saltation are invalidated by these findings.

Using a single representative particle size improves model accuracy.

Abstract

Natural wind-eroded soils contain a mixture of particle sizes. However, models for aeolian saltation are typically derived for sediment bed surfaces containing only a single particle size. To nonetheless treat natural mixed beds, models for saltation and associated dust aerosol emission have typically simplified aeolian transport either as a series of non-interacting single particle size beds or as a bed containing only the median or mean particle size. Here, we test these common assumptions underpinning aeolian transport models using measurements of size-resolved saltation fluxes at three natural field sites. We find that a wide range of sand size classes experience "equal susceptibility" to saltation at a single common threshold wind shear stress, contrary to the "selective susceptibility" expected for treatment of a mixed bed as multiple single particle size beds. Our observation of equal susceptibility refutes the common simplification of saltation as a series of non-interacting single particle sizes. Sand transport and dust emission models that use this incorrect assumption can be both simplified and improved by instead using a single particle size representative of the mixed bed.