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

Abstract

Turbulent 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.

Comparison Between Eddy‐Covariance and Flux‐Gradient Size‐Resolved Dust Fluxes During Wind Erosion Events

“…We cannot exclude that a part of the dissimilarity observed between dust and momentum turbulent transport could be also explained by the limited depth of the dust internal boundary layer due to the small fetch of our plot for some of the events, as demonstrated numerically by Fernandes et al. (2020).…”

“…The match between EC and FG-diss dust fluxes for fine and medium-size particles is less improved for March events, the EC dust flux being slightly larger than the FGdiss flux. We cannot exclude that a part of the dissimilarity observed between dust and momentum turbulent transport could be also explained by the limited depth of the dust internal boundary layer due to the small fetch of our plot for some of the events, as demonstrated numerically by Fernandes et al (2020).…”

Multi-model ensemble projection of global dust cycle by the end of 21st century using CMIP6 data

“…Strong winds and the associated pressure systems promote the momentum of surface layer and consequently increase dust mobilizations (Li et al, 2022). The transport of dust aerosols is related to atmospheric circulation and turbulent mixing, which determine the horizontal and vertical distribution of dust aerosol particles, respectively (Zhang et al, 2014;Fernandes et al, 2020). The deposition process includes dry and wet settlement, in which the dry deposition is an effective way to remove large particles while wet deposition dominates the removal of fine particles (Breuning-Madsen and Awadzi, 2005;Yue et al, 2009).…”