Aeolian Research最新文献

Suspended dust particles in atmosphere have adverse impacts on environment, ecosystem as well as on human health. To avoid negative impacts of dust storm events, early warning system to predict it well in advance may be a suitable option. However, for this purpose, assessment on magnitude of dust load and its dynamics in atmosphere is a primary requirement. The present study aims to develop remote sensing based assessment of dust load in atmosphere specifically over the Indian Thar Desert region. The severe dust storm event occurred on 5^th June 2017 over the Indian Thar Desert has been used in this study to develop integrated dust detection algorithm using split window technique, mid-infrared technique and different dust indices derived from MODIS and INSAT-3D data. Evaluation of the developed algorithm revealed that the area classified under dust load depends on threshold value of dust indices used in the algorithm, type of dust detection techniques followed and the specifications of remote sensing sensors used to retrieve the dust image. The integrated dust detection algorithm developed in this study has the capability to eliminate the problem in variations of predicted dust loadings in atmosphere. Validation of the developed algorithm to detect dust pixels showed good agreement with independent observations on aerosol optical depth (AOD), wind speed profile data and ground visibility data. The method adopted can be helpful to implement an operational system for detection and monitoring of dust storms over the Thar Desert region.

Foredune trough blowouts are elongated wind-eroded depressions in the most seaward dune and their adjoining depositional lobes. Despite their importance to the sand budget and floral diversity of coastal dunes, the spatiotemporal evolution of trough blowouts is not well understood. We designed an automated workflow in the Google Earth Engine platform to produce time series of blowout surface area from medium-resolution satellite imagery available since the mid-1980s and applied it to a blowout system in the Netherlands, Denmark and the USA. Blowout surface areas were found to vary on multi-annual, seasonal and episodic time scales. Multi-annual change reflects successive development through stages of growth, stabilization and decay. The transition from growth to stabilization appears to be related to a change in blowout shape (width-to-length ratio). The decay phase starts with vegetation obstructing the blowout connection to the beach; the lobe can still migrate inland and develop into a parabolic dune before also becoming fully vegetated. The seasonal variations in blowout area increase with latitude; the observed larger areas in winter at the Dutch and Danish site presumably reflect seasonal plant development and the effect of stronger winds in winter. Episodic increases in blowout area, observed during winter at the Danish site only, are associated with pronounced foredune erosion. None of the episodic events changed blowouts into a different stage or persistently affected seasonal dynamics. Future work should focus on the combined analysis of changes in blowout area and sand volume to improve our understanding of sand-vegetation interactions driving blowout dynamics.

A late Quaternary red sandy sediment called the Old Red Sand is widely distributed in coastal South China. Most studies have considered it a single sand body composed of wind-transported beach sand. However, the Old Red Sand also contains silt and clay. To determine the implications of this fine fraction for the origin of the Old Red Sand, four sections were studied using various depositional analyses. Under a scanning electron microscope, quartz particles in the fine fraction are well rounded, with abundant aeolian marks on their surfaces. The grain size is homogeneous and comparable to that of typical loess. The diffuse reflectance spectroscopy results suggest a higher content of haematite than goethite within the fine fraction, indicating subaerial deposition without strong hydration. The geochemical composition of the fine fraction is close to that of the upper continental crust and comparable to that of typical aeolian deposits, indicating the extensiveness of material sources, with terrestrial dust being fully mixed by wind over a large area. The depositional characteristics, sedimentary environment and provenance of the fine fraction are markedly different from those of the coarse fraction, which is composed of near-source beach sand. Therefore, the Old Red Sand is not a deposit with a single source. Both near-source coarse beach sand and exotic fine dust contributed to the formation of the deposit in the late Pleistocene, especially the last glacial period. The fine fraction is a key factor contributing to the cementation and redness of the sand body.

We imaged the near-surface sedimentary structures of a large linear dune, flanking dune forms and an associated crossing linear dune never before studied in the northern Namib Sand Sea using 200-MHz Ground-Penetrating Radar (GPR). The dry, uniform sandy conditions and wavelength used allowed for highly detailed observations of sedimentary structures to depths of ∼ 12 m across a >1km lateral scan. Sedimentary features observed in the main linear dune include scouring and abrupt changes in strata such as trough cross stratification (TCS), onlap, downlap, truncation and avalanche-related bedding, all a result of complex sand transport conditions. Different phases of deposition have produced an opposed succession of strata on each side of the dune. These successions alternate 2-dimensional (2D), or bedform instability mode features with 3-dimensional (3D), or fingering mode features, separated by a clear process boundary. These alternating successions reflect a change in the dominant wind environment in the recent past. The changing winds may feed into the building and overall stability of this dune field and may be a model for conditions in other large linear/longitudinal dune fields. The subsurface structure of an oblique crossing linear dune demonstrates sand transport generally down the dune long axis in the direction predicted from modern, ERA-Interim model as well as paleoclimate model winds. This suggests relatively long-term stability of this intermediate-sized landform and the potential long-term coexistence of large dunes and secondary forms. These studies have implications for the extensive sand seas of Titan, where lack of large secondary forms may indicate a simple wind regime over long time periods.

We present a model study of the aeolian saltation process where sediment samples are studied for the size selective transport processes. The discrete element method is used to simulate the sediment particles of different sizes, coupled with a fluid boundary layer model to capture the driving wind forces. Sediment samples with identical median grain size, but with systematically varying size distributions were simulated to investigate under various wind shear rates which sediment fractions are transported. The presented model results show - well in line with other research - that the median grain size is an appropriate sediment sample parameter to quantify the total rate of sediment transport. However, our results show that this does not determine what fractions of sediment are in transport. The larger the standard deviation in the sediment size distribution the smaller the median grain size becomes of the sediment that is in transport compared to the median grain size present at the bed.

Identifying the geochemical composition of desert sands in the Gurbantunggut Desert is essential for understanding the formation of desert dunes in the mid-latitudes. In this study, we collected samples of desert sands (125–250 μm), fluvial sands, and lacustrine sands across the Gurbantunggut Desert and calculated the sand drift potential at four meteorological stations. The sand samples from the Gurbantunggut Desert were mostly enriched in SiO₂, while the other major elements were depleted compared to those of the Upper Continental Crust (UCC). The chemical weathering indices (α^AlE, CIA, and WIP) indicate that the sand-sized sediments in the Gurbantunggut Desert are in the initial stage of continental chemical weathering. SiO₂ and K₂O contents as well as mineralogical maturity of the desert sands increased from the piedmont to the desert center. UCC-normalized distribution patterns were also consistent along this transect due to the homogenization of desert sand composition, whereas the concentrations of other major elements (except for TiO₂ and MnO) decreased. We conclude that (1) regional variations in the composition of the Gurbantunggut Desert sands primarily reflect differences in provenance, transport, sorting, recycling of the sediments, and vegetation cover as well as the chemical weathering; and (2) differences in indices describing the major element composition of the sands reflect regional variations in provenance from the mountains to the depositional basin. Sands within piedmont rivers possess major element characteristics similar to those of dune sands in the region, suggesting that rivers represent a significant source of sands in the desert.

Knowledge of the provenance of dust deposits in the easternmost margin of the Eurasian loess belt is essential for understanding the connection between circulation patterns and dust source-to-sink route in the Songnen Plain, NE China. Here, a total of 131 samples, from the loess-paleosol sequence since the last glacial (20) and the modern dust-storm sediments (7) in Harbin area together with potential dust source areas (104), were collected for elemental geochemical analysis to quantify the source apportionment and compare the performance of the Frequentist and Bayesian models. Fourteen geochemical properties (V, Zn, Ga, Sr, Mo, Ba, Pb, Y/Ta, MREE_N/MREE_N*, Th/Sc, Th/U, La/Sc, Zr/Hf and Co/Th) were selected as the optimum composite fingerprint after a range test, non-parametric Kruskal-Wallis H-test and stepwise discriminant function analysis. Based on both the models, the source contributions to the loess sequence and dust-storm deposits were in the following order: southwestern Songnen Sandy Land (57–95%, 49–97%), Horqin Sandy Land and Onqin Daga Sandy Land (2–43%, 0–31%), northwestern Songnen Sandy Land (0–21%, 0–20%) and Hulun Buir Sandy Land (0%, 0–8%). Following the goodness-of-fit and virtual mixtures, combined with root mean square error and mean absolute error, we argue that the Frequentist model is slightly more accurate than the Bayesian model in quantifying dust sources. The sandy lands figure importantly in acting as a dust transfer station. The comparison between the loess sequence and modern dust-storm source reconstructions reveals a decoupling between circulation pattern (northwesterly wind domination in the glacial) and dust path (dominantly southwestern direction), and small areas, high vegetation coverage and topographical barrier are considered to be the main reasons for the significantly limited dust emission in the NW-direction source area. Finally, the study highlights that improving land management practices in the SW-direction but not NW-direction sandy land may help ameliorate the effects of the Harbin dust pollution.

Barchan morphometric data have been used as proxies of meteorological and topographical data in environments where this data is lacking (such as other planetary bodies), gaining insights into barchan dune field dynamics such as barchan collision and sediment dynamics, and estimating migration speeds. However, manual extraction of this data is time-consuming which can impose limits on the spatial extent and temporal frequencies of observations. Combining remotely sensed big data with automated processing techniques such as convolutional neural networks (CNNs) can therefore increase the amount of data on barchan morphology. However, such techniques have not yet been applied to barchans and their efficacy remains unknown. This study addresses this issue by evaluating the classification performance (using the ACC, F 1 -score and MCC metrics) of CNNs on several different morphometric tasks: the side of horn elongation, the magnitude of elongation, the barchans a/c ratio, and a new metric, bilateral asymmetry, which takes a more holistic view of barchan asymmetry. Specifically, bilateral asymmetry offers a means by which the total points of variation on a barchan that is used in describing barchan morphology, can be expressed with a single measure. Twelve different CNN architectures, each with different hyperparameters, are trained and tested on a sample of 90 barchan dunes. Additionally, the potential of transfer learning is assessed using the VGG16 and ResNet50 architectures. The results show that the accuracy of the CNNs can exceed 80% in some cases and that “from scratch” CNNs can match the performance obtained using transfer learning approaches.

The development of coastal dunes is linked to environmental controls such as sea-level variability, climatic conditions, and coastal morphology. Understanding the spatial and temporal variations of dunes is crucial for predicting how coastal landscapes may react to future climate changes and sea-level rise. However, there are very few detailed studies on the longer time-scale evolution (centennial to millennial) of coastal dunes from subtropical and tropical regions. Here, we combine a high-resolution luminescence chronology with sedimentological analyses to study the depositional history of a transverse coastal dune located within the Bang Berd dune field, Western Gulf of Thailand. While luminescence dating of uniform aeolian deposits is normally straight forward, we observe strong variations in the natural dose rate which are likely explained by the enrichment of accessory minerals in some laminae. Deposition of the dune started at least around 3000 years ago and coincides with a regional sea level drop. Sedimentary structures indicate deposition occurring predominantly in relation to the northeasterly winter monsoon. As the sea-level rise and increased storm intensity in the future may lead to stronger erosion along the coast, this study is highlighting the importance of the Bang Berd dune system as natural protection against coastal inundation.

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.