Aeolian Research最新文献

Snow drift which usually occurs in conjunction with snowfall can significantly alter the distribution pattern of snow cover around roads creating travel hazards for vehicles. To study the snow distribution around a road and evaluate the snow prevention efficiency of snow fence, based on the theories of two-phase flow and snowdrift erosion and deposition, a numerical model is developed. The model includes snowfall during snow drift, spatial distribution characteristics of wind speed and snow phase volume fraction, and dynamic changes of snow drift shape on the ground during drifting. We simulate the distribution characteristics of snowdrift around an embankment without and with the protection of a snow fence and under the conditions of no snowfall and snowfall. The results indicate that snow deposition is greatest on the leeward side of the embankment in comparison to the windward side of the embankment and takes a longer time to reach equilibrium. On the leeward side of the embankment, the snow accumulation rate under the condition of snow falling is higher than that under the condition of no snow falling. Nonetheless, the two conditions both suggest that installation of the snow fence intercepts a large amount of snow behind the snow fence, decreases the snow phase volume fraction near the ground, and reduces the snowdrift accumulation on the leeward side of the embankment within a certain period.

Vegetation cover on coastal sand dunes has been increasing worldwide since at least the 1940s. Analysis of aerial and satellite imagery has been the principal source used to measure this change, however no studies have systematically evaluated the accuracy of remotely sensed estimates. Using established land cover classification methods and in-situ field measurements, we show that both the extent and accuracy of remotely sensed areas of bare sand and vegetation in dunes varies with image resolution and classification method. We found that supervised methods of classification (semi-automatic), whilst mapping a greater extent of bare sand and being more accurate than manual digitisation, had poor repeatability, exhibiting a relatively large range of bare sand and vegetation extent between classifications replicated under the same conditions. In contrast, areas of bare sand and vegetation classified by manual digitisation had high repeatability but a relatively low percentage of observed agreement with data collected in the field. For all classification methods, observed agreement with field data generally increased with image resolution. Our results demonstrate that users of land classification data in dunes should be cautious when interpreting trends of bare sand and vegetation cover due to substantial repeatability error in supervised classification methods, and relatively poor observed agreement with field data of manual classification. We recommend that analysis of bare sand and vegetation cover in dunes should be based on multiple replicates using supervised classification, employing the highest resolution imagery available and that all results presented should also include the range measured by multiple replicates.

The aim of this study was to describe the constructive details of a new collector called Mendeźs Trap (MT) and to compare its performance with the Big Spring Number Eight (BSNE) and Modified Wilson and Cook (MWAC). A detailed description of the MT with dimensions, schemes, and photos is included in the paper. To evaluate the performance of the MT, eleven wind erosion events were measured with MT, BSNE, and MWAC installed at 22.5, 43, 63, 112, and 164 cm height on a loamy sand soil without cover and roughness. The material collected was weighed and divided by the inlet area to obtain the horizontal mass flux (HMF). Results showed that the HMF measured with MT is strongly correlated to the HMF measured with BSNE and MWAC. Relative efficiencies (slope of the regression curve between HMF of different samplers) showed that MT is 31.83% more efficient than BSNE and that MWAC is 81.37% more efficient than MT. Different relative efficiencies were measured at different heights, but no relationships between the relative efficiency and height were found. The average amounts of material collected were the highest at 22.5 cm height (1.74 g for MT) and the lowest at 164 cm height (0.03 for MWAC). At all heights, the amounts of sediments collected were ordered in the sequence MT > BSNE > MWAC. Percentages of samples weighing more than 0.1 g, 0.2 g, 0.3 g, 0.4 g, 0.5 g were ordered in the sequence MT > BSNE > MWA. Field evaluation showed that, the HMF measured with MT, BSNE, and MWAC can be compared, and MT can be used in wind erosion studies. MT collects more amounts of material than MWACs and BSNEs, which is especially important at greater heights where little amounts of material are normally collected. The results of this study must be confirmed in soils of other texture classes and the role of the particle size and wind speed in the efficiency of the MT must be measured in wind tunnel.

While anthropogenic pollutants have decreased during the lockdown imposed as an effort to contain the spread of the Coronavirus disease 2019 (COVID-19), changes in particulate matter (PM) do not necessarily exhibit the same tendency. This is the case for the eastern Arabian Peninsula, where in March–June 2020, and with respect to the same period in 2016–2019, a 30 % increase in PM concentration is observed. A stronger than normal nocturnal low-level jet and subtropical jet over parts of Saudi Arabia, in response to anomalous convection over the tropical Indian Ocean, promoted enhanced and more frequent episodes of Shamal winds over the Arabian Peninsula. Increased surface winds associated with the downward mixing of momentum to the surface fostered, in turn, dust lifting and increased PM concentrations. The stronger low-level winds also favoured long-range transport of aerosols, changing the PM values downstream. The competing effects of reduced anthropogenic and increased dust concentrations leave a small positive signal (<5 W m⁻²) in the net surface radiation flux (R_net), with the former dominating during daytime and the latter at night. However, in parts of the Arabian Gulf, Sea of Oman and Iran R_net increased by >20 W m⁻² with respect to the baseline period, owing to a clearer environment and weaker winds. It is concluded that a reduction in anthropogenic emissions due to the lockdown does not necessarily go hand in hand with lower particulate matter concentrations. Therefore, emissions reduction strategies need to account for feedback effects in order to reach the planned long-term outcomes.

Vertical profiles of wind-blown sand as a function of the grain size are significant to better understand the microscopic process of heterogeneous saltation. Here, vertical flux density and frequency profiles of wind-blown sand as a function of the grain size over three typical gobi surfaces during three transport events were revealed. The results indicate that given the three gobi surfaces examined, the sand flux density of smaller sand particles (69–316 μm) exponentially decayed with the height, while the sand flux density of larger grains (363–976 μm) gradually deviated from the above exponential decay with the height and exhibited nonmonotonic variation with the height. The frequency of coarse grains (209–976 μm) continuously increased with the elevation until an inflection occurred at a certain height above the ground (0.17–1.3 m), and above the inflection point, the frequency of coarse grains exponentially decreased with the height. However, the frequency of fine grains (67–163 μm) initially decreased with the elevation. This trend was reversed at heights ranging from 0.17 to 0.73 m above the ground, after which the frequency exponentially increased. In contrast, the frequency profile of ∼180-μm diameter sand grains revealed an exponential decay curve throughout the entire elevation range examined. These results indicate that grains larger than 180 μm participated in the grain-bed collision process over gobi, and the rebound height was positively related to the grain size, while grains smaller than 180 μm were more notably affected by turbulence.

Grain size analysis is a powerful tool for determining the depositional environment. Grain size analysis for 48 samples from four sections along a 280 km long, nearly north–south-trending transect, has been conducted in the mainly Holocene Kordofan Sand in the Kordofan Region of Central Sudan. In these sections, this part of the Kordofan Sand comprises three pedosedimentary sequences. The lower sequence (∼13–10 kyr) has been pedogenized during the African Humid Period and ends up farther West with lacustrine or palustrine carbonates. The middle sequence (∼6–3 kyr) is represented by sand with low degree of pedogenesis and corresponds to the African Humid Period. The upper sequence was deposited after a hiatus lasting from ∼3.3 to 1.1 ka BP, and constitutes the present-day surficial deposits, showing little or no pedogenesis. Spatial grain size distribution and mode of transport show a southward fining trend, indicating that the sandy sediments were transported from north to south. This interpretation is supported by the results of mean grain size – sorting, and sorting – skewness interrelations, which provided a linear relationship. Vertical variation in grain size distribution in the studied sections shows variable energy over time in the north and constant, low energy in the south. The dominance of saltation as a transport mode confirms that the studied sediments were deposited in aeolian environment. The low sorting degree, the presence of coarse grains, and the still active transverse dunes and barchans in the North, indicate that the Late Pleistocene part of the Kordofan Sandstone is submitted to reworking until now. Consequently, the mainly Holocene sand sequences were fed both by distal, fine-grained Saharan material and by proximal, coarser-grained sand proceeding from the Late Pleistocene aeolian dunes.

The dynamic process of dust emission from gobi is a largely un-solved scientific question while it is essential for minimizing the dust hazards. In this study, field wind tunnel experiments have been performed to reveal the processes of dust emission from gobi on the top of the Mogao Grottoes. We found that the dust content of gobi is the dominant factor that determines the intensity of dust emission. The vertical PM10 flux increased exponentially with the increase of dust content on the gobi surface at a given wind speed. The impact energy of saltating particles is another control factor of the dust emission flux. The vertical PM10 flux due to saltation bombardment of the external sand supply was 5–13 times larger than that without the bombardment of sand supply. This study indicates that gobi on the top of the Mogao Grottoes is one of the main dust sources as it has an abundance of sand supply from Mingsha Mountain as well as its richness in dust content. Hence, it is imperative to expand the existing sand control system on the top of the Mogao Grottoes in order to minimize the impact of dust hazards on the Mogao Grottoes.

Wind erosion of agricultural soils affects their stock of essential elements for plants, like phosphorus (P). It is known that the composition of the eroded sediments varies with height, according to the size and density of the transported substances. Aim of this study was to analyze the concentration and enrichment ratios of P forms in sediments transported by the wind. A wind-tunnel study was performed on a sandy- and a sandy loam soil in order to measure P forms concentrations in the saltating sediments. P concentrations were also measured in the particulate matter (PM) of each soil, gained with the Easy Dust Generator. In both soils, inorganic- (P_i) and organic P (P_o) were preferentially transported in PM, with enrichment ratios of 1.8 and 5.5, respectively. Nevertheless, a P_i/P_o of 0.9 indicated that the accumulation of the minor P_o in PM was more pronounced than P_i. This agrees with P-rich light and easily erodible organic compounds, almost exclusively accumulated in PM, and in relatively heavy and less erodible minerals, like apatites, in lower height sediments. Labile P (P_l) was preferentially transported in saltating sediments of both soils. This was attributed to the selective Bray & Kurtz I’s extraction of the abundant inorganic P forms of these sediments. Total P (P_t) copied the transport trends of P_i, the major form. According to the transporting trends, P_i and P_o would be re-sedimented at longer distances from the source than P_l. Outcomes become useful for modeling the influence of wind erosion on P cycling.

Airborne particulate matter (APM) is a complex mixture of dust, dirt, soot and smoke containing both organic and inorganic components as well as biological particles. APM below 10 µm can enter the respiratory track and are known to cause adverse health effects. African dust storms are responsible for the transport of large amount of APM across the Atlantic Ocean during summer months. Anthropogenic activities are also responsible for APM pollution contribution in coastal areas and could have potential effects on sensitive ecosystems. The present study evaluates the elemental composition of APM collected from a coastal area in South Florida. In this study, a high-volume air sampler equipped with Versapor filters and located near the Port of Fort Lauderdale was employed for APM collection from 2005 to 2010. APM chemical composition was analyzed for multiple elements by ICP-MS. Seven of the eleven metals listed by the EPA as hazardous air pollutants (Mn, Cd, Cr, Ni, Pb, As, Co and Se) were detected in the samples. Iron and aluminum were the most abundant elements found in all samples, followed by V and Ni, which are usually associated with anthropogenic pollution coming from fossil fuel combustion. Specific sources of APM pollution were identified by principal component analysis and using the U.S. EPA UNMIX model for environmental data analyses. Rare earth elements were used to identify contributions of geological material to the APM and African dust influence during the summer months.

In this study, daily-mean total and dust aerosol optical depth (TAOD, DAOD, respectively) obtained from the Monitoring Atmospheric Composition and Climate (MACC) and meteorological fields from ERA-Interim reanalysis are used to identify spatial patterns of dust accumulation over northeast Iran and Karakum Desert during 2003–2012. The most dust-affected area is defined using highest variances of DAOD by S-mode and weather clusters by T-mode principal component analysis (PCA). Six weather clusters are classified via the statistical analysis, associated with high DAOD values, with larger frequency in spring, while PC1 (41 cases) dominates in summer. The results show that changes in the intensity and expansion of the Siberian/European high-pressures in spring modulate strong northeasterlies or northwesterlies over Central Asia, which are associated with frontal dust storms over the desert areas (Aralkum, Karakum). In addition, dynamic conditions associated with the sub-tropical jet stream and the Iranian trough, and combined with convective conditions at areas of thermal lows in east Iran, create a strong southwesterly wind – called Qibla – over the Iranian Plateau. These two contrasting wind regimes converge over northeast Iran/Karakum Desert, facilitating dust accumulation over the area. In summer, northerly winds dominate over Central Asia, but the absence of Qibla flow allows them to traverse till the north coast of the Arabian Sea, where they converge with the southwest monsoon flow. The accumulation of dust over northeast Iran/Karakum is lesser than that over Pakistan and Thar desert. Furthermore, the upper-level sub-tropical jet stream moves northward in summer, with core over Turkmenistan/Uzbekistan.