Origins of Turbulent Transport Dissimilarity Between Dust and Momentum in Semiarid Regions

Abstract

AbstractTurbulent transport of mineral dust away from erodible plots is usually assumed similar to the momentum transport. However, observations from the WIND‐O‐V (WIND erOsion in presence of sparse Vegetation's) 2017 field experiment over an isolated flat surface in Tunisia showed a dissimilar turbulent transport between dust and momentum. Here, the origin of this dissimilarity is explored from a numerical experiment using a detailed physically based erosion model based on a large‐eddy simulation airflow model. Simulations support the findings of the WIND‐O‐V campaign, confirming the key role played by the dust emission intermittency to the transport dissimilarity with the momentum, this later one being more continuously absorbed at the surface. Simulations reveal that this dissimilarity diminishes with height as the intermittency of dust emission is progressively lost during the turbulent transport‐mixing process. With wind intensity, the dissimilarity diminishes as well, with dust emissions becoming more spatially homogeneous, and thus less intermittent. Our simulations further highlight the additional role played by the fetch length limitation of the erodible plot to the turbulent transport dissimilarity. In presence of a short fetch, the dissimilarity between dust and momentum turbulent transports increases with height as the dust flux footprint integrates dust emission conditions from different surrounding surfaces. This latter process depends on the characteristics of the surrounded surfaces and is expected to be significant in semiarid regions.