Aeolian Research最新文献

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.

The formation and development of blowouts is an important surface indication of sand drift activity in semiarid grassland areas; thus, an accurate understanding of their morphological evolution characteristics and dynamic processes is of significance for grassland desertification control. This study analyzed the long-term topographic change of a trough blowout developed on a fixed sand dune in the Otindag sandy land of China via ground measurements from 2011 to 2020 and examined the short-term airflow structure through field observations. The results indicated that the area of the deflation basin shows a state of continuous growth. The expansion of the deflation basin was most obvious on the western, southwestern and southern slopes, which is contrary to the regional prevailing wind direction. As airflow passes over the blowout, there is significant airflow steering with the change in topography, and the degrees of airflow steering and acceleration are determined by the direction of the approaching wind. Airflow expands and decelerates on the leeward side of the deflation basin, causing flow separation and producing a recirculation zone on the sheltered lee slopes. Based on a detailed analysis of the results, we suggest that the soil collapse and sand avalanches caused by vortices are the main reasons for the upwind expansion of the deflation basin. Collectively, these findings reveal a strong link between the blowout morphology and the airflow pattern.

Wedge dunes are widespread on Mars and contain important information about Mars surface processes and environmental characteristics. These dunes are wedge-shaped in plan-view, similar in scale to a barchan dune, with two slip faces intersecting at an obtuse angle and extending outward toward the main ridge downwind. And, the length of its main ridge does not exceed its width. At present, our understanding of wedge dunes and their development in nature is limited. The type, morphology, distribution and spatial composition of wedge dunes on Mars and Earth were investigated using high-resolution satellite image data. The results reveal that wedge dunes are simple in type and similar in size to barchan dunes. Martian wedge dunes are similar in shape to terrestrial wedge dunes but larger in size. The average angles between the sub-ridges of Martian and terrestrial wedge dunes are similar, at about 116°. Martian wedge dunes are mainly located in Abalos Undae, Siton Undae, and Aspledon Undae in the North Polar region, accounting for about 5% of the total area covered by dune fields. Wedge dunes are rare on Earth and can only be found on the edge of a few contiguous dune fields. These dunes indicate acute bimodal or obtuse bimodal wind regimes. Wedge dunes have distinct transitional characteristics and may be the initial stage of the development of various dune patterns. The implications of these findings are discussed, in particular the periodic changes in the regional wind direction reflected by the wedge dunes, as well as the significance of the distinctive transitional features of the wedge dunes for improving our understanding of the genesis of complex dune patterns.

Frontal dust storms are rare but important weather events in southern Iran affecting visibility and air quality, especially in urban areas. This study investigated the main characteristics of the 13 May 2018 frontal dust storm in Shiraz. The evaluation was based on geostatistical models, and mineralogical, elemental and isotopic data. The mean and median concentrations of major and trace elements followed the order Ca > Al > Fe > Mg > K > Na > Ti > Mn > Zn > V > Cr > Ni > Cu > Pb > Co > Cd, in agreement with the mineralogical composition of dust samples. The spatial distributions of the potentially toxic elements (PTEs) show that the concentrations were higher in the central sectors of city, likely due to the higher population density and traffic volume. Integrated source characterization coupled with positive matrix factorization (PMF) identified that the PTEs sources were geogenic, anthropogenic, and sea salt related. Geochemical isotopic methods, δ¹⁸O and δ¹³C values along with hybrid single-particle Lagrangian integrated trajectory (HYSPLIT) analysis suggest that the dust storm mainly originated from Saudi Arabia. However, local lithological units and resuspended street dust also played an important role in the elemental distributions. These results also indicate that combining various datasets can be beneficial in characterizing the sources of dust storms and their components in southwestern Iran.

The Keeler Dunes Complex is an active dune field located on the northwest corner of Owens (dry) Lake, California. Previous studies (Lancaster and McCarley-Holder, 2013) implicated the exposed surface of the Owens River Delta as the source of sediment for the Keeler Dunes based on the calculation of the Resultant Drift Potential (RDP). Measurements from sand flux monitoring stations located between the Owens River Delta and Keeler Dunes were used to determine the accuracy of using RDP for estimating actual sand transportation. It was found that the net average direction of sand transportation in this area (133°) was not accurately predicted by RDP (97°). Therefore, prior conclusions based on RDP erroneously attributed sediment from the Owens River Delta as a source for the Keeler Dunes. Since RDP calculations are widely used and a convenient method for determining the direction and magnitude of net sand transportation based on meteorological measurements, methods for modifying the RDP to achieve better agreement with sand flux measurements are desirable. Two modifications were found to improve the agreement between calculated RDP and measured sand transportation: 1) accounting for temporal variability in sediment availability (RDP = 130°), and 2) utilization of an area-specific threshold friction velocity (RDP = 129°). Combining these two modifications also resulted in good agreement (RDP = 137°) with the measured sand transportation but did not improve agreement further. These findings suggest that information about surface characteristics (sediment availability and surface roughness) are important to consider when estimating sand transportation based on wind energy.

Dune fields on the Southern High Plains such as the Monahans in West Texas are archives of Quaternary environmental variability. Stratigraphic analyses and sixty-one optically stimulated luminescence (OSL) ages from seven Geoprobe cores and one section from the Monahans reveal a ∼ 550 ka old aeolian sedimentary record with seven carbonate/argillic paleosols and a playa-lake margin deposit. OSL ages on quartz-grains from aeolian sediments by two protocols, single aliquot regeneration (SAR) and thermal transfer (TT), yield congruent ages between 50 and 250 ka, and the oldest ages of ca. 550 ka, potentially minima. This chronostratigraphic analysis and finite-mixture modeling of the OSL-age distribution identify-four aeolian depositional periods (ADP) at 545 to 475, 300 to 260, 70 to 45, and post 16 ka and possibly-two additional ADPs 460 to 420 ka and 350 to 320 ka. Playa lake deposits identified west of the Monahans and correlative to carbonate-rich paleosols indicate that wetter conditions prevailed during interglacial MIS 7, 235 to 195 ka. Another wetter period, 25 to 16 ka, with the formation of Lake King in the adjacent Rio Grande Valley is correlative with a pedogenically-modified <2 m-thick aeolian sand. This study underscores that there may be multiple climatic states, during glacials and interglacials, associated with wetter conditions. In turn, the thickest, preserved aeolian deposits are associated with transitional climate periods, penecontemporaneous with stadials, when the Laurentide ice sheet was <80 % of the last glacial maximum volume, with precipitation-bearing zonal circulation shifted northward and weakened meridional moisture flux.

Accurate description of the characteristics of erosion and deposition around single model plants of different shapes is important to evaluate the protective role of plants in wind erosion control. The variation of bed topography with time was measured in a wind tunnel for two flexible models and two rigid tree-like models. The bed surface height close to the plant decreases forming a deep well, while in the lee, a deposition area generally appears whose shape is affected by plant type. The local wind erosion rate on both sides usually decreases with time, and the deposition area in the lee with the local erosion rate less than zero gradually moves downwind with time while disappears for the tree-like plant model with a long trunk and a large crown. Under similar frontal areas of plants, both the erosion and deposition areas around the tree-like plant with a short trunk and conical crown, and the flexible plant with a large upper part and a small lower part are generally larger than that around the slender flexible plant. The rigid tree-like plant with a short trunk and a dense conical crown is better for erosion control due to the smallest net erosion rate and the erosion area similar to the deposition area, while the other plant models have larger net erosion rate and much larger erosion area.