Aeolian Research最新文献

The paper presents the development, adaptive improvement and use of the method to estimate the wind erosion risk in Germany for Cross Compliance (CC) regulations, based on the German standard DIN19706. It is illustrated by the example of the Federal State of Brandenburg. A landscape structure model was developed which calculates the sheltering effects of landscape elements. Basic inputs are the heights of all landscape elements and the frequencies and directions of erosive winds. In combination with the soil map of erodibility the wind erosion risk is derived in a high spatial resolution according to the CC requirements. In addition to improving the input data in terms of its spatial resolution by using air-borne laser scanning data, an innovative approach is presented which derives the sheltered areas behind landscape elements from the transport capacities of wind speeds above a threshold. Thus, our analysis represents one of the most comprehensive wind erosion assessment of cropland that can be used for landscape structure assessment well beyond CC use. The derivation of effective protection zones from the frequencies of erosive winds when critical thresholds are adjusted represents an innovative approach that provides an objective and transferable assessment of wind protection of landscape features in different wind regimes.

Aeolian dune movement poses a threat to critical infrastructure, urban areas, water resources as well as agriculture. This threat is expected to increase in the coming years due to land degradation, desertification and climate change. Several approaches have been used to investigate the evolution of dune fields. Satellite remote sensing can be considered one of the most accurate tools for the continuous monitoring of global sand covered surfaces. Although early studies found a great potential in synthetic aperture radar (SAR) for dune assessment, the full potential has not been explored as of yet. Therefore, in this study, we present a novel method for assessing complex dune field morphology based on the easily accessible and globally available Sentinel-1 ground range detected (GRD) SAR dataset. In this application, dune features are extracted based on backscatter properties related to the local incidence angle. This provides a clear identification of (1) active dune sand, (2) dune ridges and (3) inter-dune ripples. By extracting these features through profiles, the multi-timescale evolution of the Western Mongolian dune field Bor Khyar was analysed through three areas of interest (AOIs) based on the spectral technique of continuous wavelets. The result of this investigation gives new insights into the temporal and spatial dynamics of dunes scale and their response to aeolian activity, revealing differences in aeolian activity as well as inter- and intra-annual variations in the dune morphology. These results are promising and highlight the potential in using satellite SAR imagery for dune monitoring.

The foreland of the Russian Altai is dominated by the vast Ob loess plateau. The flat landscape exhibits striking linear features, partially more than 100 km in length and tens of km wide. The bottoms of these features are covered by forested dunes, whereas the loess ridges in between are intensively cultivated. To the north, the land cover changes due to gradual transition from the steppe towards the Siberian taiga. The genesis of these prominent features was debated within the last decades. Possible explanations cover tectonic lineaments, fluvial erosion, and landforms caused by outbursts of catastrophic floods from the Altai Mountains. Here, we present geomorphological evidence for the aeolian origin of these features based on field observations and geodata. These large lineaments do not show characteristic features of fluvial valleys, since the shape of the lineaments is too straight and does not show braided river characteristics as, e.g., the Ob or the Irtysh valley. The sheer size of these features also does not support the hypothesis of tectonic activity or a catastrophic flood since events like this would be imprinted in other environmental archives of the region. We show that these linear landforms show remarkable similarities with Pleistocene mega yardang systems throughout the world. These systems can usually be found in arid to hyper-arid environments, but were also described in, e.g., mid-latitude regions. We hypothesis that the Pleistocene glaciations of the Altai Mountains enhanced the strength and the influence of the westerlies in the Altai forelands. Therefore, we propose an erosive-aeolian origin of these remarkable landforms.

Buildings at the beach change the near-bed airflow patterns in the surrounding area. This induces alterations in wind-induced bed shear stress and wind-induced sediment transport which, in turn, affect the bed topography in the vicinity of buildings. Three-dimensional computational fluid dynamics simulations using OpenFOAM have been performed to understand how and to what extent the buildings at the beach influence the sediment transport from the beach to the dunes. Herein, we explicitly account for the positioning of the buildings with respect to each other and the dominant wind direction. Also discussed are the airflow mechanisms that are responsible for sediment transport, and how they alter due to systematic changes in the gap spacing between buildings and the wind incidence angle. Simulations were performed, in which we model flow and initial sediment transport around a repeating row of ten parallel full-scale beach buildings when the gap spacings and wind incidence angles were systematically varied. The horizontal near-bed streamline patterns showed that there is a critical gap spacing, below which the neighboring buildings significantly affect each other. Furthermore, the airflow in the near-wake region behind the row of buildings is quite complex. The shape and the extent to which the sand drifts develop behind the gaps between buildings are largely influenced by the wind direction, relative to the buildings. We also computed the average sediment transport flux along different lines downstream of the buildings. Our findings showed that, depending on the buildings’ positioning at the beach, they could have negative effects on dune growth by obstructing the sediment particles from moving downstream, or they could have positive effects on dune growth by steering the airflow and supplying more sediment downstream.

In recent decades, there has been a divergence in the evidence (models, observations, reanalysis data) about the trend of coastal upwelling driving winds in the current global warming scenario over the Humboldt Current System. Herein, we present a 150 yr, sub-decadal grain size distribution record of a laminated sediment core (B0405-6) retrieved from the continental shelf of the Pisco region (∼14 °S) within the wind-driven coastal upwelling system of South-Central Peru. This area is characterized by local aeolian inputs from seasonal dust storms called Paracas Winds (PW). This study aims to reconstruct the variability of surface wind intensity using the Geometric Median Diameter (GMDs) and frequency (A%) of aeolian particles in a high temporal resolution sediment core and to unravel the mechanisms that control this variability. In addition, we propose to evaluate these GMDs as a better proxy of local surface wind strength and thus the variability of upwelling favorable winds (UFWs) in these near-source conditions. Our results show a progressive intensification of the UFWs in the region throughout the last 150 years, which agrees with other records along the South Pacific coast. In addition, good correspondence was found between the UFW wind proxy and the region's sea surface temperature (SST) trends, suggesting an intensification of the driving mechanisms linked to these events. It also suggests that UFW intensification could continue as the local coastal atmospheric jet strengthens. A comparison of indirect oceanic and atmospheric records from the South American Pacific coast is shown at the regional scale, suggesting a recent progressive expansion and intensification of the South Pacific Subtropical High (SPSH).

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.

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.

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.

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.