Natural dust is often associated with hot, subtropical deserts, but significant dust events have been reported from cold, high latitudes. This review synthesizes current understanding of high‐latitude (≥50°N and ≥40°S) dust source geography and dynamics and provides a prospectus for future research on the topic. Although the fundamental processes controlling aeolian dust emissions in high latitudes are essentially the same as in temperate regions, there are additional processes specific to or enhanced in cold regions. These include low temperatures, humidity, strong winds, permafrost and niveo‐aeolian processes all of which can affect the efficiency of dust emission and distribution of sediments. Dust deposition at high latitudes can provide nutrients to the marine system, specifically by contributing iron to high‐nutrient, low‐chlorophyll oceans; it also affects ice albedo and melt rates. There have been no attempts to quantify systematically the expanse, characteristics, or dynamics of high‐latitude dust sources. To address this, we identify and compare the main sources and drivers of dust emissions in the Northern (Alaska, Canada, Greenland, and Iceland) and Southern (Antarctica, New Zealand, and Patagonia) Hemispheres. The scarcity of year‐round observations and limitations of satellite remote sensing data at high latitudes are discussed. It is estimated that under contemporary conditions high‐latitude sources cover >500,000 km2 and contribute at least 80–100 Tg yr−1 of dust to the Earth system (~5% of the global dust budget); both are projected to increase under future climate change scenarios.

McKeNNn-NeuMAN, C. AND NrcKLrNG, W. G. 1989. A theoretical and wind-tunnel investigation of the effect of capillary water on the entrainment of sediment by wind.Can. J. Soil A theoretical model of the effect of small amounts of water on the threshold shear velocity of sand grains has been tested in wind-tunnel studies. The model is based upon the capillary forces developed at interparticle contacts surrounded by isolated wedges of water. These forces (F") are inversely proportional to moisture tension (P) and directly proportional to the geometric properties of the contacts (G). Given F": rT2GlP, the cohesion of the material decreases with increasing moisture tension and particle angulariry. F,:2r R2T + r R.rz T,n -*j, (4) where R1 is the radius of the air-water interface and R2 is the radius of the "waist" of the water wedge (Fig. 1) Haines (1925) and Fisher (1926) for spheres predict a sharp drop in capillary force with increasing moisture content up to l0% by mass.

Abstract:Since the pioneering work of Bagnold in the 1940s, aeolian research has grown to 1 become an integral part of earth-system science. Many individuals have contributed to this 2 development, and Dr. Michael R. Raupach (1950Raupach ( -2015 has played a pivotal role. Raupach 3 worked intensively on wind erosion problems for about a decade (1985 -1995)

[1] Direct bed level observations of surface shear stress, pressure gradient variability, turbulence intensity, and fluid flow patterns were carried out in the vicinity of cylindrical roughness elements mounted in a boundary layer wind tunnel. Paired corkscrew vortices shed from each of the elements result in elevated shear stress and increased potential for the initiation of particle transport within the far wake. While the size and shape of these trailing vortices change with the element spacing, they persist even for large roughness densities. Wake interference coincides with the impingement of the upwind horseshoe vortices upon one another at a point when their diameter approaches half the distance between the roughness elements. While the erosive capability of the horseshoe vortex has been suggested for a variety of settings, the present study shows that the fluid stress immediately beneath this coherent structure is actually small in comparison to that caused by compression of the incident flow as it is deflected around the element and attached vortex. Observations such as these are required for further refinement of models of stress partitioning on rough surfaces.

Volcaniclastic dust particles are characterized by unique physical properties, which are speculated to influence their rates of entrainment, emission and deposition within the atmospheric boundary layer. Few detailed particlescale measurements exist, so that natural particles often are idealized as solid glass spheres in the parameterization of dust dispersion models. This study shows that volcaniclastic dust particles from Iceland contain substantial quantities of amorphous glass, large internal voids and copious dustcoats comprised of nano-scale flakes. Their high porosity, found to increase with particle diameter, generates particle densities that can be substantially lower than expected for a solid sphere. An abundance of volcanic glass also seems to increase particle porosity and roughness, and thereby strongly correlates with the Brunauer Emmett Teller surface area. An analysis based on Stokes' law further suggests that Icelandic dust with a standardized geometric diameter (10 μm or PM 10), but with varying density, shape and origin, may have settling velocities in still air that are up to 20% lower than for a reference glass sphere. As a first approximation, neglecting complex particle interactions and wind speed, which also affect the deposition rate in the atmosphere, their low density and large surface area could increase the expected residence time by a factor of five. Model parameterization should be refined to incorporate these particle-scale factors in order to improve on the estimation of volcaniclastic dust dispersion.