Gentle Topography Increases Vertical Transport of Coarse Dust by Orders of Magnitude

Abstract

Dust particles emitted in the atmosphere are responsible for numerous phenomena of global consequence here on Earth. In particular, coarse dust (with diameter greater than 5 μm) absorbs shortwave and longwave radiation which contributes to warming of the planet (Kok et al., 2017), redistributes mineral nutrients such as iron and phosphates to ocean (Jickells et al., 2014) and land ecosystems (Swap et al., 1992) through its long-range transport, and alters the nucleation of clouds and their subsequent precipitation (Mahowald & Kiehl, 2003).Given the importance of coarse dust to local and global processes, it is critical for models to accurately represent coarse dust concentrations. Yet there is a consistent disparity between measured observations and global dust models, where models severely underestimate the presence of coarse dust (Adebiyi &

Improved Parameterization for the Size Distribution of Emitted Dust Aerosols Reduces Model Underestimation of Super Coarse Dust

“…Second, the vertical transport of (super) coarse dust might be underestimated. In particular, a recent study has shown that topography greatly enhances the upward vertical transport of super coarse dust in the boundary layer (Heisel et al., 2021 ). This effect is not fully accounted for in most models and could help explain the remaining slight underestimation of super coarse dust near source regions (Figures 1b and 2 ).…”

A review of coarse mineral dust in the Earth system

“…In these schemes the nonlocal eddy diffusivity represents turbulent properties characteristic of the PBL. Models may underestimate the altitude of coarse particles in the PBL, i.e., before they are subject to long-range transport, due to limitations in PBL mixing schemes and/or the omission of phenomena such as the effect of subgrid scale topography upon their vertical mixing (e.g., Rosenberg et al, 2014;Heisel et al, 2021). This could be the case, e.g., for the very deep mixing layer over the Sahara in summer (Garcia-Carreras et al, 2015).…”

A review of coarse mineral dust in the Earth system

“…Consequently, aircraft measurements indicate that topography can strongly enhance the vertical transport of super-coarse and (especially) giant dust particles (Rosenberg et al, 2014). Large Eddy Simulations confirm this finding and indicate that the enhanced vertical transport of super-coarse and giant dust occurs because of a number of factors, including upward flow on the uphill slope driving vertical transport and increased vertical dispersion in the wake of crests (Heisel et al, 2021). Most of these processes affecting the emission and vertical transport of super-coarse and giant dust are not represented in current model parameterizations of dust emission, which likely underestimate the emission of super-coarse dust (Huang et al, 2021;Kok et al, 2021a), although an updated parameterization of the emitted dust size distribution using brittle material fragmentation seems to at least partially resolve this problem (Meng et al, 2022).…”

“…In these schemes the non-local eddy diffusivity represents turbulent properties characteristic of the PBL. Models may underestimate the altitude of coarse particles in the PBL, i.e., before they are subject to long-range transport, due to limitations in PBL mixing schemes and/or the omission of phenomena such as the effect of subgrid-scale topography upon their vertical mixing (e.g., Rosenberg et al, 2014;Heisel et al, 2021). This could be the case, e.g., for the very deep mixing layer over the Sahara in summer (Garcia-Carreras et al, 2015).…”