Aeolian Research最新文献

The determinants controlling the particle size distribution (PSD) of emitted dust in the atmosphere during erosion events are still poorly understood despite the significant impact of mineral dust on meteorology and air quality. Here, we report dust emission flux PSD from a plot in Tunisia during two consecutive erosion seasons, using the same measurement set-up and method to estimate size-resolved dust fluxes. The first year, the plot was a bare soil while the second year the plot was sparsely vegetated, the vegetation covering less than 2% of the plot. Surprisingly, the emitted dust flux PSD exhibited significant variation along the second-year erosive season, with overall a larger proportion of submicron particles, differing from the more constant PSD during the first year erosive season. We show that this PSD variation of the dust flux during the second year is not explained by the presence of the vegetation nor by the atmosphere wind-dynamic and thermodynamic conditions. The emission transfer velocity of dust particles appears independent of the particle size and constant during and between both erosive seasons. We rather suggest that this PSD variation can only be explained by modifications of the soil surface conditions depending on surface tillage and soil humidity during the erosion season, both impacting the available soil aggregates and inter-particle cohesion. This result highlights the crucial role played by the soil surface conditions on the PSD of emitted dust fluxes.

Zibar is an Arabic word for aeolian bedforms that are coarse-grained, of limited relief, have no slipfaces, and occur on sand sheets and within interdune corridors of many sand seas. They may also be called granule-armored dunes, undulations, transverse aeolian ridges, mega-ripples, giant ripples, and chevrons and whalebacks. Zibars, though very extensive, are by no means ubiquitous in the world’s aeolian environments. They occur in thirteen main locations in dry, warm deserts: Algodones, USA; Gran Desierto, Mexico; eastern Mauritania; Ubari, Libya; Libyan Desert; Erg of Fachi-Bilma/Tenéré; Selima, Sudan; Namib, Namibia; Lut, Iran; southern Rub’ al Khali, Arabia; Thar, India; Kumtagh, China; and Atacama, Peru. They can occur as transverse ridges, as parabolic shapes, and as oblique features. In many regions they tend to have a spacing of around 8 to 14 per km. They tend to be modest in height, varying between tens of centimeters to up to c 6–8 m. All researchers seem to agree that they are mound-like forms without slipfaces and that their slope angles are no more than 5-15^o_. Nearly all zibars occur in the interdunes between various types of linear dune. They are composed of ill-sorted sand, often with a large coarse component.

The long-term evolution of coastal sand-dune systems is known to be controlled by variations in sediment supply, relative sea level (RSL), wind energy, vegetation cover and anthropogenic forcing. The link between episodic sand invasion and changes in climate conditions (enhanced storminess) has been previously evidenced along the Atlantic coasts of Europe from stratigraphical, geomorphological and chronological investigations of recent aeolian sand-dune deposits. While well-constrained timing templates of dune accretion during Holocene were reconstructed in Portugal, Spain and Ireland, available data about the French Atlantic coast are limited to the Aquitaine dune complex (SW France). This lack of data is mainly due to the absence of well-developed palaeosoils interbedded within the aeolian sand deposits, especially in Brittany where only thin humic layers are preserved within the coastal dune sediment sequences. An alternative approach is here applied to the coastal dunes of Brittany by also integrating available and partly revised archaeological dataset, excavated from the end of the 19th century, and used as chrono-stratigraphical markers to reconstruct at a regional scale the periods of coastal dunes mobility during the last ca. 6000 years. This analysis was further combined with historical data (historical syntheses, archives, old maps, historical photos) about the last few centuries. 221 sites distributed along the western coasts of France have been selected to provide accurate information in terms of dune stratigraphy and chronology. A conceptual tool routinely used in archaeology, the Harris matrix, was employed to synthesise these chrono-stratigraphic data about 78 coastal sand-dune systems. Four main episodes of aeolian activity identified during the mid- to late-Holocene period are dated at 4250–4100 cal BP (phase 1), 3250–2400 cal BP (phase 2), 1050–700 cal BP (phase 3), and 350–110 cal BP (phase 4). Despite some methodological limitations, archaeological remains appear to be relevant chronological indicators and may be used to reconstruct ancient periods of coastal dune mobility. Finally, an evolutionary model is established about the sand-dune morphological changes that occurred during the mid-to late-Holocene period along the Western France coasts and the nature of the driving mechanisms of sand movement initiation is also discussed.

Mineral dust particles suspended in the atmosphere span more than three orders of magnitude in diameter, from <0.1 µm to more than 100 µm. This wide size range makes dust a unique aerosol species with the ability to interact with many aspects of the Earth system, including radiation, clouds, hydrology, atmospheric chemistry, and biogeochemistry. This review focuses on coarse and super-coarse dust aerosols, which we respectively define as dust particles with a diameter of 2.5–10 µm and 10–62.5 µm. We review several lines of observational evidence indicating that coarse and super-coarse dust particles are transported farther than previously expected and that the abundance of these particles is substantially underestimated in current global models. We synthesize previous studies that used observations, theories, and model simulations to highlight the impacts of coarse and super-coarse dust aerosols on the Earth system, including their effects on dust-radiation interactions, dust-cloud interactions, atmospheric chemistry, and biogeochemistry. Specifically, coarse and super-coarse dust aerosols produce a net positive direct radiative effect (warming) at the top of the atmosphere and can modify temperature and water vapor profiles, influencing the distribution of clouds and precipitation. In addition, coarse and super-coarse dust aerosols contribute a substantial fraction of ice-nucleating particles, especially at temperatures above –23 °C. They also contribute a substantial fraction to the available reactive surfaces for atmospheric processing and the dust deposition flux that impacts land and ocean biogeochemistry by supplying important nutrients such as iron and phosphorus. Furthermore, we examine several limitations in the representation of coarse and super-coarse dust aerosols in current model simulations and remote-sensing retrievals. Because these limitations substantially contribute to the uncertainties in simulating the abundance and impacts of coarse and super-coarse dust aerosols, we offer some recommendations to facilitate future studies. Overall, we conclude that an accurate representation of coarse and super-coarse properties is critical in understanding the impacts of dust aerosols on the Earth system.

Wind erosion occurs in arid and semi-arid regions and causes surface erosion, dust and environmental threats. Despite research on the formation of biological surface crust on coarse-grained soils via the MICP process, as an alternative method to prevent and reduce desertification and dust, a few studies have been conducted on clay soils. The current research adopted the biological dust control technique using the Bacillus pasteurii microorganism in silt and clay soils in Meighan Wetland, Iran, which consists of specific salt and minerals. The treated soil specimens were exposed to a wind tunnel for 7, 14, 28, 56 and 140 days in order to measure surface erosion. To determine the effect of the amount of bacteria on the MICP method, the bacteria concentrations of 50 % and 100 % and amount of bacteria on the surface 1 and 2 lit/m² were investigated. To further investigate the effect of soil modification with bacteria on the specimens, cone penetration, acid washing, scanning electron microscopy, and X-ray diffraction tests were carried out. The results showed that according to the conditions of the study area, the use of MICP method and the creation of biological crust in the scope of the current study was an effective and environmentally friendly procedure. By using this method, the surface resistance of silt and clay samples in the region has increased by 95 % and 80 %, respectively. In addition, the use of the MICP method leads to the reduction of wind erosion of silt and clay samples by 90 % and 98 %, respectively.

Evaluating the ability of natural surfaces to generate wind driven dust emissions into the atmosphere is essential to the development and refinement of local to regional and global emissions models and the assessment of environmental hazards posed by windblown dust. Close to 3,900 individual PM₁₀ emission tests were conducted with the Portable-In Situ Wind ERosion Laboratory (PI-SWERL) between fall 2015 and spring 2021 on exposed Salton Sea playa and adjacent desert areas, California, United States. Each test location was also evaluated for surface characteristics and geomorphological unit. On playa surfaces, the crust type, presence of loose, erodible surface sand, soil moisture, and percent crust cover were found to have significant effects (P < 0.001) on PM₁₀ emission potentials. On desert surfaces, PM₁₀ emission potential varied significantly between geomorphic landforms (P < 0.001). In general, PM₁₀ emission potentials tended to be higher for desert landforms and less variable compared to playa surfaces. Highly emissive surfaces were generally dry and had sufficient loose surface sand to initiate and sustain saltation and the associated liberation of dust-sized particles. Surfaces characterized by low dust emissions exhibited moist conditions, stable crusts, or gravel lag deposits. The geometric mean potential emission rates ranged over two orders of magnitude, with a low and high of 4 and 398 μg m⁻² s⁻¹ (at an RPM of 3,000 or a u_* range of 0.56–0.73 m s⁻¹). Based on differences in surface area and emission potentials, the overall dust emissions in the study domain are dominated by emissions from desert sources.

North American observed atmospheric dust has shown large variability over the last two decades, coinciding with regional patterns of vegetation and wind speed changes. Dust emission models provide the potential to explain how these direct causes of vegetation and wind speed changes are related to changing dust emission. However, those dust models which assume land cover types are homogeneous over vegetation classes and fixed over time, are unlikely to adequately represent changing aerodynamic roughness of herbaceous cover, woody cover, and litter. To overcome these model limitations and explain changing (2001–2020) dust emission, we used a new MODIS albedo-based dust emission model calibrated to satellite-observed magnitude and frequency of dust emission point source (DPS) data. We focused our work on four regions of southwestern USA, identified previously as the main dust emission sources. We classified the interplay of controlling factors (wind speed and aerodynamic roughness) which created disturbance regimes with dust emission change consistent with diverse land use and management drivers. Our calibrated model results show that dust emission is increasing or decreasing, in different regions, at different times, for different reasons, consistent with the absence of a secular change of observed atmospheric dust. Our work demonstrates that using this calibrated dust emission model, sensitive to changing vegetation structure and configuration and wind speeds, provides new insights to the contemporary factors controlling dust emission. With this same approach, the prospect is promising for modelling historical and future dust emission responses using prognostic albedo in Earth System Modelling.

In this paper, Large Eddy Simulation (LES) of turbulence and Lagrangian model of sand particle motion are adopted to study the characteristics of wind-blown sand flow for different boundary layer thickness. The simulations are conducted within computational domain height (boundary layer thickness) of δ = 0.5 m, 1 m, 5 m and 12 m, respectively. It is found by comparing the computational results that the mass flux and sand transport rate increase with the increase of boundary layer thickness for the same frictional wind velocity, and the fluctuation of particle velocity and sand transport rate increase significantly too. The spatial scales of particle structure, defined by the correlation of sand particle concentration, significantly increase with δ, so does the time scale of statistical stability of sand transport rate. For two computational domains of δ = 1 m and 12 m, the statistical relative error of sand transport rate reduce to less than 5 % only when the average time goes higher than 45 δ/U_b, where U_b is the bulk fluid velocity. In the context of turbulence, it might take about 10 mins to obtain reliable sand statistics in the neutral atmospheric boundary layer whose boundary layer thickness is about 100–200 m.

We present initial results of an investigation into meteorological and geological controls on the formation of dust devils (i.e., dust-filled vortices formed in the daytime dry convective boundary layer). During a 2-week field campaign in June 2019 at Smith Creek Valley (SCV), Nevada, USA, we conducted automated time-lapse stereo imaging of dust devils (DDs), while monitoring local meteorological conditions with a broad suite of instruments. Counts of imaged dust devils from two near-cloudless days were compared with a standard suite of atmospheric measurements from a weather tower, eddy correlation flux measurements, and ceilometer backscatter returns. DDs forming in moderate winds (5–8.5 m/s) were more likely to be relatively wide and disorganized, with qualitatively low dust opacity, whereas those forming in weaker winds were more likely to be coherent, dusty, well-formed conical or cylindrical structures. The daily maximum DD counts at SCV occurred shortly after their onset in late morning (11:00–12:00 local time), coinciding with a surge in CBL growth that was likely delayed by the thermal properties of the playa. This late morning peak contrasts with previous studies conducted elsewhere that typically observed peak DD counts in the afternoon. As observed in previous field studies, DDs formed in highly convective conditions, when the heat flux ($H$) and friction velocity ($u_{\ast }$) were elevated and the convective ratio $w_{\ast }/u_{\ast }$ exceeded ∼ 4 (i.e., $-h/L$ exceeded ∼ 25). However, values of>4$w_{\ast }/u_{\ast }$ also occurred in mid-morning, prior to DD formation and CBL growth, suggesting that this metric is not the sole condition required for DD generation. Aside from the late morning maxima, DD counts fluctuated considerably throughout the afternoon at timescales of 0.5–2  h–correlating poorly with fluctuations in $H$ and $u_{\ast }$, and not at all with either $w_{\ast }/u_{\ast }$ or the Monin-Obukhov length ($L$). Several factors, such as local variations in surface thermal properties and meteorology, may be responsible for these short-term fluctuations.

Buildings affect aeolian sediment transport and bedform development in sandy environments. Cellular automaton (CA) models have, however, only been used to simulate natural bedform dynamics. This study extends a well-known aeolian CA model to include sediment dynamics around buildings, and uses this model to explore the interaction of building-induced deposition and erosion with natural bedform dynamics. New CA rules are introduced to represent acceleration, deceleration and sideward transport of sediment around obstacles. The simulated deposition and erosion patterns show good agreement with field experiments. The model reproduces the shape and location of the morphological pattern around a single building, and effects of building spacing on this pattern for building groups. Model results further demonstrate that building-induced effects interact with local bedform dynamics and can alter the shape, growth and migration of sand dunes.