Earth and Planetary Sciences › Earth-Surface Processes

Aeolian processes and effects

Works Count: 44363

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Description

This cluster of papers explores the dynamics of aeolian processes, including wind erosion, sand dune formation and mobility, the impact of vegetation cover, and the influence of climate change on desert landscapes. It also delves into the interactions between aeolian and fluvial systems, dust emission, and the geomorphological effects of windbreaks.

Keywords

Aeolian Processes; Wind Erosion; Sand Dunes; Dune Dynamics; Vegetation Cover; Climate Change; Sediment Transport; Desertification; Coastal Dunes; Dust Emission

Aeolian Sand and Sand Dunes

2008-11-13

Kenneth Pye , Haim Tsoar

Atmospheric Boundary Layer Flows

1994-03-10

J. C. Kaimal , John Finnigan

Boundary layer meteorology is the study of the physical processes that take place in the layer of air that is most influenced by the earth's underlying surface. This text/reference gives … Boundary layer meteorology is the study of the physical processes that take place in the layer of air that is most influenced by the earth's underlying surface. This text/reference gives an uncomplicated view of the structure of the boundary layer, the instruments available for measuring its mean and turbulent properties, how best to make the measurements, and ways to process and analyze the data. The main applications of the book are in atmospheric modelling, wind engineering, air pollution, and agricultural meteorology. The authors have pioneered research on atmospheric turbulence and flow, and are noted for their contributions to the study of the boundary layer. This important work will interest atmospheric scientists, meteorologists, and students and faculty in these fields.

Aeolian Dust and Dust Deposits

1987-01-01

Kenneth Pye

Sedimentary structures, their character and physical basis

1984-01-01

J. R. L. Allen

NEOTECTONICS OF A STRIKE-SLIP RESTRAINING BEND SYSTEM, JAMAICA

1985-01-01

Paul Mann , Grenville Draper , Kevin Burke

Introduction to Micrometeorology

1988-01-01

S. Pal Arya

Water capture by a desert beetle

2001-11-01

Andrew R. Parker , Chris R. Lawrence

Jamming is not just cool any more

1998-11-01

Andrea J. Liu , Sidney R. Nagel

Horizontal dispersion of floatable particles in the vicinity of velocity singularities such as convergences

1970-06-01

Akira Ōkubo

Characterization and Distribution of Water-repellent, Self-cleaning Plant Surfaces

1997-06-01

Christoph Neinhuis

During the last 20 years, a wealth of data dealing with scanning electron microscopy of plant surfaces has been published. The ultrastructure of epidermal surfaces has been investigated with respect … During the last 20 years, a wealth of data dealing with scanning electron microscopy of plant surfaces has been published. The ultrastructure of epidermal surfaces has been investigated with respect to taxonomic, as well as functional aspects. Within the latter, water-repellency has received much attention and has been well documented. Water-repellency is based on surface roughness caused by different microstructures (trichomes, cuticular folds and wax crystals), together with the hydrophobic properties of the epicuticular wax. In addition, contaminating particles are carried away by water droplets, resulting in a cleaned surface (Lotus-effect). Therefore, rough, waxy leaves are not only water-repellent but anti-adhesive with respect to particulate contamination. Based on 200 water-repellent plant species, the present paper surveys micromorphological characteristics of anti-adhesive plant surfaces. Leaves that are permanently water-repellent can be differentiated by distictively convex to papillose epidermal cells and a very dense layer of epicuticular waxes. Leaves that are water-repellent for only a limited period of time have only slightly convex epidermal cells and often have a less dense wax layer. Finally, an overview is given on the occurrence of water-repellency among different life forms and within different habitats. Water-repellency is concentrated in herbaceous species, while it is rare in trees. Among different habitats, subtropical regions, wetlands and disturbed areas appear to have more species with water-repellent leaves. The importance of roughness and water-repellency, respectively, as the basis of an anti-adhesive, self-cleaning surface, in comparison to other functions of microstructures, is discussed.

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The physics of wind-blown sand and dust

2012-09-14

Jasper F. Kok , Eric J. R. Parteli , Timothy I. Michaels +1 more

The transport of sand and dust by wind is a potent erosional force, creates sand dunes and ripples, and loads the atmosphere with suspended dust aerosols. This paper presents an … The transport of sand and dust by wind is a potent erosional force, creates sand dunes and ripples, and loads the atmosphere with suspended dust aerosols. This paper presents an extensive review of the physics of wind-blown sand and dust on Earth and Mars. Specifically, we review the physics of aeolian saltation, the formation and development of sand dunes and ripples, the physics of dust aerosol emission, the weather phenomena that trigger dust storms, and the lifting of dust by dust devils and other small-scale vortices. We also discuss the physics of wind-blown sand and dune formation on Venus and Titan.

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Simplified expressions for vegetation roughness length and zero-plane displacement as functions of canopy height and area index

1994-10-01

Michael Raupach

The deepening of the wind-Mixed layer

1973-03-01

Raymond T Pollard , Peter B. Rhines , Rory O. R. Y. Thompson

AbstractA simple model is given that describes the response of the upper ocean to an imposed wind stress. The stress drives both mean and turbulent flow near the surface, which … AbstractA simple model is given that describes the response of the upper ocean to an imposed wind stress. The stress drives both mean and turbulent flow near the surface, which is taken to mix thoroughly a layer of depth h, and to erode the stably stratified fluid below. A marginal stability criterion based on a Froude number is used to close the problem, and it is suggested that the mean momentum has a strong role in the mixing process. The initial deepening is predicted to obeywhere u. is the friction velocity of the imposed stress, N the ambient buoyancy frequency, and t the time.After one-half inertial period the deepening is arrested by rotadeon at a depth h = 22/4 u.{(Nf)+ where f is the Coriolis frequency. The flow is then a "mixed Ekman" layer, with strong inertial oscillations superimposed on it. Three quarters of the mean energy of the deepening layer is found to be kinetic, and only one-quarter potential.Heating and cooling are included in the model, but stress dominates for time-scales of a day or less. Non-uniform stratification and currents existing prior to the onset of the wind are easily included.Agreement between the first formula above and laboratory experiments of Kato and Phillips is very satisfactory; the second formula is consistent with observations of Francis and Stommel, though a more thorough test is needed. Oceanic observations in general support the assumption of slab-like mean profiles and direct response of the fluid to local winds.

Saharan dust in the Amazon Basin

1992-01-01

Robert Swap , M. Garstang , Steven Greco +2 more

Saharan dust is shown to enter the Central Amazon Basin (CAB) in bursts which accompany major wet season rain systems. Low-level horizontal convergence feeding these rain systems draws dust from … Saharan dust is shown to enter the Central Amazon Basin (CAB) in bursts which accompany major wet season rain systems. Low-level horizontal convergence feeding these rain systems draws dust from plumes which have crossed the tropical Atlantic under the large-scale circulation fields. Mass exchange of air between the surface and 4 km over the eastern Amazon basin is calculated using rawinsonde data collected during storm events. Mean concentrations of dust observed by aircraft over the western tropical Atlantic are used to calculate the amount of dust injected into the Basin. Individual storm events inject some 480,000 tons of dust into the north-eastern Amazon Basin. Storm and dust climatology suggest that the annual importation of dust is in the order of 13 Mtons. In the north-eastern basin, this may amount to as much as 190 kg ha-1 yr-1. Deposition of trace species, such as phosphate, associated with this dust ranges from 1-4 kg ha-1 yr-1. Uncertainties in these estimates are not believed to be greater than ± 50% and may be as low as ± 20%. The deposition fluxes from Saharan dust are essentially identical to the CAB wet deposition fluxes from precipitation in the wet season; a result that implies that the major ionic composition of rain water in the CAB wet season may be strongly influenced by inputs of material originating on the African continent nearly 5000 km away. The total amount of Saharan dust calculated to enter the Amazon basin is 1/2 to 1/3 of that estimated to cross 60°W longitude between 10° and 25°N latitude. We conclude that part of the productivity of the Amazon rain forest is dependent upon critical trace elements contained in the soil dust originating in the Sahara/Sahel. This dependence should be reflected by expansions and contractions of the Amazon rain forest in direct relationship to expansions and contractions of the Sahara/Sahel. Turnover rates for nutrient species deposited with Saharan dust in the Amazon Basin suggest a time scale of 500 to 20,000 years. We believe the dependence of one large ecosystem upon another separated by an ocean and coupled by the atmosphere to be fundamentally important to any view of how the global system functions. Any strategy designed to preserve the Amazonian rain forest or any part thereof should equally concern itself with the inter-relationship between the rain forest, global climate and arid zones well removed from Amazonia.

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Incorporation of mineralogical composition into models of the radiative properties of mineral aerosol from UV to IR wavelengths

1999-04-01

I. N. Sokolik , O. B. Toon

We describe a technique to model the radiative properties of mineral aerosols which accounts for their composition. We compile a data set of refractive indices of major minerals and employ … We describe a technique to model the radiative properties of mineral aerosols which accounts for their composition. We compile a data set of refractive indices of major minerals and employ it, along with data on mineralogical composition of dust from various locations, to calculate spectral optical and radiative properties of mineral aerosol mixtures. Such radiative properties are needed for climate modeling and remote sensing applications. We consider external mixtures of individual minerals, as well as mixtures of aggregates. We demonstrate that an external mixture of individual minerals must contain unrealistically high amounts of hematite to have a single scattering albedo lower than 0.9 at 500 nm wavelength. In contrast, aggregation of hematite with quartz or clays can strongly enhance absorption by dust at solar wavelengths. We also simulate the daily mean net (solar + infrared) forcing by dust of varying compositions. We found that, for a given composition and under similar atmospheric conditions, a mixture of aggregates can cause the positive radiative forcing while a mixture of individual minerals gives the negative forcing.

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Effect of saltation bombardment on the entrainment of dust by wind

1993-07-20

Yaping Shao , M. R. Raupach , P. A. Findlater

Saltation is the wind‐driven, hopping motion of sand‐sized particles across an erodible surface. This mode of motion not only transports sand and similar materials in its own right but can … Saltation is the wind‐driven, hopping motion of sand‐sized particles across an erodible surface. This mode of motion not only transports sand and similar materials in its own right but can also initiate (through bombardment of the surface) the entrainment and subsequent transport by suspension of smaller dust particles. In this paper, we report a wind tunnel study of the effect of saltation bombardment on dust entrainment. The technique is to allow sand grains to saltate from an upwind sand source onto a bed of dust particles. The experiment confirms that the ejection of dust particles by saltation bombardment (as opposed to detachment of dust particles by aerodynamic forces) is the principal mechanism for the natural entrainment of dust by wind. The data are used to examine the dependence of the dust emission flux F d (mass per unit ground area per unit time) upon the friction velocity u * ; it is found that F d is closely proportional to the streamwise flux of saltating sand grains, which in turn is approximately proportional to u * 3 At a given u * , F d increases as the size of the bombarding sand grains increases. On the basis of the hypothesis that F d is proportional to the kinetic energy flux of the saltating sand grains, we derive theoretically the result that F d scales with the streamwise saltating sand grain flux and thence approximately with u * 3 , as observed in this experiment.

Ecosystems of Disturbed Ground

2000-08-01

Roger C. Anderson , Lawrence R. Walker

Hardbound. As the human population inexorably grows, its cumulative impact on the Earth's resources is hard to ignore. The ability of the Earth to support more humans is dependent on … Hardbound. As the human population inexorably grows, its cumulative impact on the Earth's resources is hard to ignore. The ability of the Earth to support more humans is dependent on the ability of humans to manage natural resources wisely. Because disturbance alters resource levels, effective management requires understanding of the ecology of disturbance. This book is the first to take a global approach to the description of both natural and anthropogenic disturbance regimes that physically impact the ground. Natural disturbances such as erosion, volcanoes, wind, herbivory, flooding and drought plus anthropogenic disturbances such as foresty, grazing, mining, urbanization and military actions are considered. Both disturbance impacts and the biotic recovery are addressed as well as the interactions of different types of disturbance. Other chapters cover processes that are important to the understanding of disturbance of all types including soil proc

Wind stress on a water surface

1955-10-01

H. Charnock

Abstract The vertical distribution of horizontal mean wind in the lowest 8 metres over a reservoir (1·6 km × 1 km) has been measured using sensitive anemometers freely exposed from … Abstract The vertical distribution of horizontal mean wind in the lowest 8 metres over a reservoir (1·6 km × 1 km) has been measured using sensitive anemometers freely exposed from a fixed mast in water 16 m deep, the fetch being more than 1 km. The resulting profiles are closely logarithmic, the small differences being systematic and possibly due to the thermal instability which existed when the measurements were made. The usual law for wind profiles in neutral stability is where u is the wind speed at height z , k is von Kármán's constant, log z (0) the intercept on the log z axis, and u * the so‐called friction velocity defined by τ 0 = pu , τ 0 being the surface drag and rH the density of the air. To characterize the profiles u * / k , their slope, was plotted in relation to z (0), their intercept; this allowed a direct comparison with other profiles, in particular those recently measured in a laboratory channel by Sibul. The agreement was better than expected and indicated that z (0) was comparatively independent of fetch and stability but was largely determined by u * . The relation between u * and z (0) agreed roughly with the simplest non‐dimensional relation between them, gz (0)/ u = constant, so that one is led to a generalized wind profile for flow over a water surface which specifies the drag, given the wind at one known height. An approximate value of the constant is 12·5. This expression can be compared with earlier work. The better wind‐profile observations show rough agreement; the experimental scatter is necessarily large since a water surface is aerodynamically much smoother than most land surfaces, precision anemometry in difficult circumstances being required to provide sufficiently precise values. Oceanographic measurements of the tilt of water surfaces are in fair agreement at high wind speeds but at low wind speeds the data are conflicting. The early results which imply that the drag‐coefficient ( u / u 2 ) increases with decreasing wind speed in light winds are thought to be in error; some support for this belief comes from recent estimates of drag using a modified ageostrophic technique, which agree roughly among themselves and with the general expression.

Late Cenozoic Glacial Ages

1972-05-01

A.E.M. Nairn

Modeling of mineral dust in the atmosphere: Sources, transport, and optical thickness

1994-11-20

Ina Tegen , Inez Fung

A global three‐dimensional model of the atmospheric mineral dust cycle is developed for the study of its impact on the radiative balance of the atmosphere. The model includes four size … A global three‐dimensional model of the atmospheric mineral dust cycle is developed for the study of its impact on the radiative balance of the atmosphere. The model includes four size classes of mineral dust, whose source distributions are based on the distributions of vegetation, soil texture and soil moisture. Uplift and deposition are parameterized using analyzed winds and rainfall statistics that resolve high‐frequency events. Dust transport in the atmosphere is simulated with the tracer transport model of the Goddard Institute for Space Studies. The simulated seasonal variations of dust concentrations show general reasonable agreement with the observed distributions, as do the size distributions at several observing sites. The discrepancies between the simulated and the observed dust concentrations point to regions of significant land surface modification. Monthly distribution of aerosol optical depths are calculated from the distribution of dust particle sizes. The maximum optical depth due to dust is 0.4–0.5 in the seasonal mean. The main uncertainties, about a factor of 3–5, in calculating optical thicknesses arise from the crude resolution of soil particle sizes, from insufficient constraint by the total dust loading in the atmosphere, and from our ignorance about adhesion, agglomeration, uplift, and size distributions of fine dust particles (<1 μm).

The nature, origin and accumulation of loess

1995-01-01

Kenneth Pye

Biological Feedbacks in Global Desertification

1990-03-02

William H. Schlesinger , James F. Reynolds , Gary L. Cunningham +4 more

Studies of ecosystem processes on the Jornada Experimental Range in southern New Mexico suggest that long-term grazing of semiarid grasslands leads to an increase in the spatial and temporal heterogeneity … Studies of ecosystem processes on the Jornada Experimental Range in southern New Mexico suggest that long-term grazing of semiarid grasslands leads to an increase in the spatial and temporal heterogeneity of water, nitrogen, and other soil resources. Heterogeneity of soil resources promotes invasion by desert shrubs, which leads to a further localization of soil resources under shrub canopies. In the barren area between shrubs, soil fertility is lost by erosion and gaseous emissions. This positive feedback leads to the desertification of formerly productive land in southern New Mexico and in other regions, such as the Sahel. Future desertification is likely to be exacerbated by global climate warming and to cause significant changes in global biogeochemical cycles.

Saharan dust storms: nature and consequences

2001-12-01

Andrew Goudie , Nick Middleton

Dust sources and deposition during the last glacial maximum and current climate: A comparison of model results with paleodata from ice cores and marine sediments

1999-07-01

N. M. Mahowald , Karen E. Kohfeld , M. Hansson +5 more

Mineral dust aerosols in the atmosphere have the potential to affect the global climate by influencing the radiative balance of the atmosphere and the supply of micronutrients to the ocean. … Mineral dust aerosols in the atmosphere have the potential to affect the global climate by influencing the radiative balance of the atmosphere and the supply of micronutrients to the ocean. Ice and marine sediment cores indicate that dust deposition from the atmosphere was at some locations 2–20 times greater during glacial periods, raising the possibility that mineral aerosols might have contributed to climate change on glacial‐interglacial time scales. To address this question, we have used linked terrestrial biosphere, dust source, and atmospheric transport models to simulate the dust cycle in the atmosphere for current and last glacial maximum (LGM) climates. We obtain a 2.5‐fold higher dust loading in the entire atmosphere and a twenty‐fold higher loading in high latitudes, in LGM relative to present. Comparisons to a compilation of atmospheric dust deposition flux estimates for LGM and present in marine sediment and ice cores show that the simulated flux ratios are broadly in agreement with observations; differences suggest where further improvements in the simple dust model could be made. The simulated increase in high‐latitude dustiness depends on the expansion of unvegetated areas, especially in the high latitudes and in central Asia, caused by a combination of increased aridity and low atmospheric [CO 2 ]. The existence of these dust source areas at the LGM is supported by pollen data and loess distribution in the northern continents. These results point to a role for vegetation feedbacks, including climate effects and physiological effects of low [CO 2 ], in modulating the atmospheric distribution of dust.

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Foredunes and blowouts: initiation, geomorphology and dynamics

2002-10-07

Patrick A. Hesp

Basic types of stratification in small eolian dunes

1977-06-01

Ralph E. Hunter

ABSTRACT The thinnest recognizable strata in modern eolian dune sands can be grouped into six classes. They are herein named planebed laminae, rippleform laminae, ripple‐foreset crosslaminae, climbing translatent strata, grainfall … ABSTRACT The thinnest recognizable strata in modern eolian dune sands can be grouped into six classes. They are herein named planebed laminae, rippleform laminae, ripple‐foreset crosslaminae, climbing translatent strata, grainfall laminae, and sandflow cross‐strata. Planebed laminae are formed by tractional deposition on smooth surfaces at high wind velocities. They are very rare in the deposits studied. Grainfall laminae are also formed on smooth surfaces, largely by grainfall deposition in zones of flow separation. They are much more common than planebed laminae, which they closely resemble. Eolian climbing‐ripple structures are composed primarily of climbing trans‐latent strata, each of which is the depositional product of a single climbing ripple. Climbing translatent strata that formed at relatively high or supercritical angles of ripple climb are typically accompanied by rippleform laminae, which are wavy layers parallel to the rippled depositional surfaces. Ripple‐foreset crosslaminae, which are incomplete rippleform laminae produced when the angle of ripple climb is relatively low or subcritical, are rarely visible in eolian sands. Sandflow cross‐strata are formed by the avalanching of noncohesive sand on dune slipfaces. Their form varies with slipface height and with other factors.

Drag and drag partition on rough surfaces

1992-09-01

Michael Raupach

A simple expression for wind erosion threshold friction velocity

2000-09-01

Yaping Shao , Hua Lu

Threshold friction velocity u *t is the friction velocity at which wind erosion is initiated. While u *t is affected by a range of surface and soil properties, it is … Threshold friction velocity u *t is the friction velocity at which wind erosion is initiated. While u *t is affected by a range of surface and soil properties, it is a function of particle size only for idealized soils. In this paper we present a simple expression for u *t for spherical particles loosely spread over a dry and bare surface. In this expression we consider the balance between the driving forces (aerodynamic drag and lift) and the retarding forces (cohesion and gravity) and assume that the cohesive force is proportional to particle size. It is found that u *t can be expressed as , with Y 1 and Y 2 being empirical constants. The new expression is both simple and effective.

Spatial and temporal characteristics of dust storms in China and its surrounding regions, 1960–1999: Relations to source area and climate

2001-05-01

Jimin Sun , Zhang Ming-ying , Tungsheng Liu

Compilation and analysis of the past 40 years of dust storm reports from China allow estimation of the meteorological conditions of dust storms, dust transport routes, and eolian source regions. … Compilation and analysis of the past 40 years of dust storm reports from China allow estimation of the meteorological conditions of dust storms, dust transport routes, and eolian source regions. Our results indicate that dust storms in China are highly associated with the frontal systems and the Mongolian cyclonic depression. The spatial distribution of dust storms indicates that there are two dominant source regions of eolian dust raised from China and its surrounding regions. The major source is the gobi deserts in Mongolia and northern China. Another source region is the Taklimakan Desert in western China. However, dust entrained from the two sources makes different contributions to downwind deposition regions. In most cases, dust materials entrained from the gobi deserts of Mongolia and China can only be entrained to an elevation of <3000 m. They are the dominant source materials of the eolian sediments in the Loess Plateau, southeastern China, offshore regions, and the near North Pacific Ocean. Dust materials from the Taklimakan Desert can be entrained to an elevation of >5000 m and then transported over long distances (∼5000 km) by the westerlies. These materials are not the main sources of the dust deposited in the proximal region, such as the Chinese Loess Plateau, but they are important sources of the eolian fraction of pelagic sediment in the remote North Pacific Ocean.

Exponentially decreasing distributions for the logarithm of particle size

1977-03-25

Ole E. Barndorff‐Nielsen

The family of continuous type distributions such that the logarithm of the probability (density) function is a hyperbola (or, in several dimensions, a hyperboloid) is introduced and investigated. It is, … The family of continuous type distributions such that the logarithm of the probability (density) function is a hyperbola (or, in several dimensions, a hyperboloid) is introduced and investigated. It is, among other things, shown that a distribution of this kind is a mixture of normal distributions. As to applications, the paper focuses on the mass-size distribution of aeolian sand deposits, with particular reference to the findings of R. A. Bagnold. The distribution family seems, however, to be of some potential usefulness in other concrete contexts too.

Desert dust suppressing precipitation: A possible desertification feedback loop

2001-05-15

Daniel Rosenfeld , Yinon Rudich , Ronen Lahav

The effect of desert dust on cloud properties and precipitation has so far been studied solely by using theoretical models, which predict that rainfall would be enhanced. Here we present … The effect of desert dust on cloud properties and precipitation has so far been studied solely by using theoretical models, which predict that rainfall would be enhanced. Here we present observations showing the contrary; the effect of dust on cloud properties is to inhibit precipitation. Using satellite and aircraft observations we show that clouds forming within desert dust contain small droplets and produce little precipitation by drop coalescence. Measurement of the size distribution and the chemical analysis of individual Saharan dust particles collected in such a dust storm suggest a possible mechanism for the diminished rainfall. The detrimental impact of dust on rainfall is smaller than that caused by smoke from biomass burning or anthropogenic air pollution, but the large abundance of desert dust in the atmosphere renders it important. The reduction of precipitation from clouds affected by desert dust can cause drier soil, which in turn raises more dust, thus providing a possible feedback loop to further decrease precipitation. Furthermore, anthropogenic changes of land use exposing the topsoil can initiate such a desertification feedback process.

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Dust transport and the question of desert loess formation

1987-02-01

Haim Tsoar , Kenneth Pye

ABSTRACT Although contemporary dust storms are frequent in arid and semi‐arid areas, desert loess deposits are poorly developed. Much of the World's loess occurs in mid‐latitude areas which experienced glaciation … ABSTRACT Although contemporary dust storms are frequent in arid and semi‐arid areas, desert loess deposits are poorly developed. Much of the World's loess occurs in mid‐latitude areas which experienced glaciation during the Pleistocene. Ocean core evidence indicates that dust transport from sub‐tropical deserts increased during cold stages of the Pleistocene, but loess formed only on certain desert margins, for reasons which have not been fully explained. This paper re‐examines the mechanisms of dust transport and deposition, and the circumstances leading to the accumulation of thick loess. Typical loess is composed mainly of medium silt grains which are transported in short‐term suspension a few metres above the ground. Significant thicknesses of loess form only when dust is trapped within a limited area, often relatively close to the source. Dust particles finer than 20 μm are transported mainly in long‐term suspension over a greater height range and may be widely dispersed. The availability of silt and the frequency, magnitude and direction of dust‐transporting winds are important factors governing the potential for loess formation, but the existence of a suitable dust trap is particularly important. Traps may be formed by topographic obstacles, areas of moist ground, or vegetated surfaces. Vegetation adjacent to glacial outwash plains and braided meltwater streams trapped dust in mid‐latitudes during the Pleistocene. Dust blown during glacial periods from certain deserts, notably in Sinai, Soviet Central Asia and China, accumulated as loess in neighbouring semi‐arid regions. On the margins of other deserts loess formation was inhibited partly by the absence of vegetation traps. During most of the Holocene net dust deposition rates in all desert‐marginal areas have been too low for significant loess accumulation. This is mainly due to a reduction in silt availability and a tendency towards landscape stability. Reported dust storm frequencies during the past 50 years over‐estimate the longer‐term Holocene dust flux due to the effects of human activities. Much modern dust owes its origin to erosion of cultivated soils in semi‐arid areas and is finer than typical loess.

Spatially averaged flow over a wavy surface

1977-04-20

J. Dungan Smith , S. R. McLean

Saltation of uniform grains in air

1964-10-01

P. R. Owen

The interaction between a turbulent wind and the motion of uniform saltating grains of sand or soil, so massive as to fail to enter into suspension, is examined on the … The interaction between a turbulent wind and the motion of uniform saltating grains of sand or soil, so massive as to fail to enter into suspension, is examined on the basis of two complementary hypotheses. The first asserts that the effect of the moving grains on the fluid outside the region to which saltation is confined is similar to that of solid roughness of height comparable with the depth of the saltation layer. The second requires the concentration of particles engaging in the saltation to adjust itself so that the shear stress exerted by the wind on the ground—different from that acting on the fluid outside the saltation layer by an amount accountable to the change in horizontal momentum suffered by the particles in their passage through the fluid—is just sufficient to maintain the sand-strewn surface in a mobile state. Existing experimental data on the wind profiles outside the saltation region and the horizontal flux of particles through it are shown to be consistent with these hypotheses. The second hypothesis implies a self-balancing mechanism for controlling the concentration of saltating particles. For if the concentration is too low the shear stress at the surface rises above the value required merely to secure mobility and more particles are encouraged to leave the surface; conversely, too large a concentration depresses the surface stress, and the consequent loss of surface mobility inhibits saltation and reduces th concentration of particles until equilibrium is restored.

Comparison of laser grain size analysis with pipette and sieve analysis: a solution for the underestimation of the clay fraction

1997-06-01

M. Konert , Jef Vandenberghe

ABSTRACT Classically, the grain size of soil and sediment samples is determined by the sieve method for the coarse fractions and by the pipette method, based on the ‘Stokes’ sedimentation … ABSTRACT Classically, the grain size of soil and sediment samples is determined by the sieve method for the coarse fractions and by the pipette method, based on the ‘Stokes’ sedimentation rates, for the fine fractions. Results from the two methods are compared with results from laser diffraction size analysis, which is based on the forward scattering of monochromatic coherent light. From a point of view of laboratory efficiency, the laser sizing technique is far superior. Accuracy and reproducibility are shown by measurements on certified materials. It appears that laser grain size measurements of certified materials correspond very well with the certificated measurements. Tests were also done on a set of randomly selected sediments of fluvial, aeolian and lacustrine origin. Except for the (<2 μm) clay fraction, there is a coarsening of the mean diameter of one to two size classes (0.25 ɛ), caused by the non‐sphericity of the particles. The platy form of the clay particles induces considerable differences (eight size classes) between pipette and laser measurements: the <2 μm grain size, defined by the pipette method corresponds with a grain size of 8 μm defined by the Laser Particle Sizer for the studied sediments. Using a higher grain size level for the clay fraction, when laser analysis is applied, enables workers in the geological and environmental field to compare classical pipette analysis with a laser sizing technique.

Northern Hemisphere atmospheric stilling partly attributed to an increase in surface roughness

2010-10-17

Robert Vautard , Julien Cattiaux , Pascal Yiou +2 more

Modeling the atmospheric dust cycle: 1. Design of a soil‐derived dust emission scheme

1995-08-20

Béatrice Marticorena , G. Bergametti

A soil‐derived dust emission scheme has been designed to provide an explicit representation of the desert dust sources for the atmospheric transport models dealing with the simulation of the desert … A soil‐derived dust emission scheme has been designed to provide an explicit representation of the desert dust sources for the atmospheric transport models dealing with the simulation of the desert dust cycle. Two major factors characterizing the erodible surface are considered: (1) the size distribution of the erodible loose particles of the soil which controls the erosion threshold and the emission strength and (2) the surface roughness which imposes the efficient wind friction velocity acting on the erodible surface. These two parameters are included in a formulation of the threshold wind friction velocity by adapting a size‐dependent parameterization proposed by Iversen and White (1982) and by applying to the rough erodible surfaces a drag partition scheme derived from Arya (1975). This parameterization of the threshold friction velocity has been included in an horizontal flux equation proposed by White (1979). This allows to attribute a specific production rate to each soil size range for each type of surface. The dust flux F is then considered as a fraction of the total horizontal flux G, the value of the ratio F/G being imposed, at this time, by the soil clay content. In summary, the computed mass fluxes depend on the soil size distribution, the roughness lengths, and the wind friction velocity. The different steps of this scheme have been independently validated by comparison with relevant experimental data. Globally, the agreement is satisfying, so that the dust fluxes could be retrieved with less uncertainties than those observed in previous simulations of the desert dust cycle.

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The flow of cohesionless grains in fluids

1956-12-18

R. A. Bagnold

Part I . The results of previous experiments (Bagnold 1954) on the stresses set up in a uniform gravity-free dispersion of solid grains when uniformly sheared in a fluid are … Part I . The results of previous experiments (Bagnold 1954) on the stresses set up in a uniform gravity-free dispersion of solid grains when uniformly sheared in a fluid are applied to the nonuniform case of grain flow over a gravity bed, assuming the results are quantitatively applicable to any sufficiently thin shear layer. It is found that if the bed is composed entirely of potentially mobile grains a stress-equilibrium relation at the bed surface can be defined whereby the magnitude of a certain ‘bed load’ of grains in transit over unit bed area is given in terms of the applied tangential stress. The bed load is independent both of the existence of any additional suspended load and of the degree of dispersion of the grains. The state of internal fluid motion enters as a single experimental constant. From a consideration of the stability of this equilibrium relation it is possible to predict the conditions under which an initially plane bed surface should become rippled; and general quantitative agreement is found with experimental data both for wind-blown and water-driven grains. Primary and secondary bed rippling are distinguished. The magnitude of the ‘form-drag’ due to primary bed ripples can be calculated. That due to secondary ripples is definable as an experimental constant. The gravity-free experiments disclosed that the shear resistance of a grain dispersion may vary as the square or the first power of the rate of shear, analogously to that of a true fluid, according to the value of a number G analogous to a Reynolds number. The square law is followed when the effects of grain inertia dominate over those of fluid viscosity. Assuming that the phenomenon of ‘saltation’ as observed over a gravity bed is an inertia effect, the conditions for saltation are predictable. The results again agree quantitatively with observation. Part II . The resistance offered by the grains to their displacement along the flow is shown to be proportional to their normal immersed weight component. And their measurable mass transport rate is hereby proportional to the rate of useful work done in transporting them. On this basis separate expressions are found for the transport rates of the bed load and suspended load, in terms of the applied tangential stress and of a tangential and a normal relative velocity respectively. When conditions are restricted to those of the ‘stream case’ these velocities become constant for any given system, being functions of an appropriate constant mean drag coefficient. The bed-load transport-rate expression found gives magnitudes, and variations of magnitude with grain size, in agreement with the experimental data for wind-blown sand. Agreement is also found for water-driven grains in open channels from the threshold of movement up to a certain value of the applied stress. The experimental rates are then found to increase suddenly. This increase is attributed to the development of an additional suspended load. The abrupt development of a suspended load may be explained as due to a change in the nature of the fluid turbulence when the stationary boundary becomes occluded from the fluid flow by a concentrated layer of moving bed-load grains. The assumption that under these new moving-boundary conditions the available fluid energy derived from shearing over the bed is equally apportioned between bed-load and suspended-load transport work leads to values for the suspended-load transport rate which agree closely with the experimental data. A critical relation emerges between the gravity slope of the bed, the fall velocity and the mean transport velocity of the suspended grains at which their transport may become very large. Conditions are examined under which the steady transport may be possible of grains of heterogeneous size or density. Part III . When the fluid flow is non-inertial (laminar) and the grain flow is also non-inertial the semi-empirical relations found previously for the internal stresses are such that both viscosity and shear rate can be eliminated, and a differential equation obtained whose solution gives the grain concentration in terms only of distance from the bed and of the applied tangential stress. It appears that with constant applied stress (unlimited flow depth) the degree of grain dispersion greatly exceeds that to be expected in turbulent fluid flow. But when the applied stress diminishes linearly with distance from the bed boundary a possible solution gives constant grain concentration throughout the flow. This appears to explain certain experimental results, including the behaviour of ‘slurries’. The effect is examined of a fixed or partially fixed bed on the grain flow in a turbulent fluid. The effect may be pronounced in the case of suspended grains. Under certain clearly definable conditions a loose grain bed must cease to remain stationary. And if the fluid flow above is turbulent the whole grain bed should flow at constant maximum concentration, underneath the flow proper and separated from it by a moving-bed surface interface at which the concentration is discontinuous. This explains phenomena sometimes found under river torrents. The factors giving rise to and limiting the development of bed features (dunes) on a bigger scale than ripples are examined. Dune formation appears as an inherent tendency of the grain flow alone, which may or may not be inhibited by the conditions of the fluid flow.

The Physics of Blown Sand and Desert Dunes

1941-10-01

H. HEYWOOD

Mechanical composition of clastic sediments

1914-01-01

Jon Andreas Udden

Research Article| January 01, 1914 Mechanical composition of clastic sediments JOHAN AUGUST UDDEN JOHAN AUGUST UDDEN Search for other works by this author on: GSW Google Scholar GSA Bulletin (1914) … Research Article| January 01, 1914 Mechanical composition of clastic sediments JOHAN AUGUST UDDEN JOHAN AUGUST UDDEN Search for other works by this author on: GSW Google Scholar GSA Bulletin (1914) 25 (1): 655–744. https://doi.org/10.1130/GSAB-25-655 Article history received: 14 Oct 1914 first online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Twitter LinkedIn Tools Icon Tools Get Permissions Search Site Citation JOHAN AUGUST UDDEN; Mechanical composition of clastic sediments. GSA Bulletin 1914;; 25 (1): 655–744. doi: https://doi.org/10.1130/GSAB-25-655 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search nav search search input Search input auto suggest search filter All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract IntroductoryIn an earlier paper2 I have published mechanical analyses of a number of samples of wind sediments and have described the conditions under which these samples were formed, classifying them into lag gravels, drifting sand, lee sand, and atmospheric dust. It was my purpose to present some reliable measurements on the mechanical composition of such deposits. It was evident from that study that wind sediments are less heterogeneous in their mechanical make-up than water sediments are. This fact is quite generally recognized. It is readily inferred from consideration of the physical forces and conditions involved. The lightness of the air prevents it from moving pebbles more than about one centimeter in diameter, except on occasions so rare that wind deposits of that coarseness are practically non-existent. Likewise, dust grains measuring less than one sixty-fourth millimeter in diameter are so easily held in the atmosphere that they are readily scattered . . . This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not currently have access to this article.

Physics and Modelling of Wind Erosion

2008-10-12

Yaping Shao

Climatic Impact of Tropical Lowland Deforestation on Nearby Montane Cloud Forests

2001-10-19

Robert O. Lawton , U. S. Nair , Roger A. Pielke +1 more

Tropical montane cloud forests (TMCFs) depend on predictable, frequent, and prolonged immersion in cloud. Clearing upwind lowland forest alters surface energy budgets in ways that influence dry season cloud fields … Tropical montane cloud forests (TMCFs) depend on predictable, frequent, and prolonged immersion in cloud. Clearing upwind lowland forest alters surface energy budgets in ways that influence dry season cloud fields and thus the TMCF environment. Landsat and Geostationary Operational Environmental Satellite imagery show that deforested areas of Costa Rica's Caribbean lowlands remain relatively cloud-free when forested regions have well-developed dry season cumulus cloud fields. Further, regional atmospheric simulations show that cloud base heights are higher over pasture than over tropical forest areas under reasonable dry season conditions. These results suggest that land use in tropical lowlands has serious impacts on ecosystems in adjacent mountains.

Aeolian sand and sand dunes

1990-01-01

Kenneth Pye , Haim Tsoar

The spectrum of horizontal gustiness near the ground in high winds

1961-04-01

A. G. Davenport

Abstract Results of a study of about 70 spectra of the horizontal components of gustiness in strong winds are described. From these and other published data the following expression for … Abstract Results of a study of about 70 spectra of the horizontal components of gustiness in strong winds are described. From these and other published data the following expression for the spectrum of gustiness for strong winds in the lower layers is suggested: magnified image Cross‐spectra and cross‐correlations of velocity between pairs of stations on a mast are given. From this it appears that the cross‐spectra can be expressed as a simple function of the ratio of the vertical separation to the wavelength, no dependence on height being detectable.

The Physics of Blown Sand and Desert Dunes

1941-08-01

Hui Kho J. , R. A. Bagnold

Evaluation of the Influence of Wind-Induced Dune Movement on Transmission Tower Lines

2025-06-25

Shijun Wang , Wenyuan Bai , Yunfei Tian +2 more | Atmosphere

Thorough investigation into dune morphology is pivotal for grasping the intricacies of constructing and operating power transmission lines in desert terrains. However, there remains a notable gap in the quantitative … Thorough investigation into dune morphology is pivotal for grasping the intricacies of constructing and operating power transmission lines in desert terrains. However, there remains a notable gap in the quantitative analysis and assessment of how dune dynamics evolve under the influence of transmission infrastructure. In this study, the Real-Space Cellular Automaton Laboratory is deployed to explore how transverse dunes evolve around transmission towers under diverse wind velocities and varying dune dimensions. The results reveal that, beyond the immediate vicinity of the transmission tower, the height of the transverse dune remains largely stable across broad spatial scales, unaffected by the transmission line. As wind velocities wane, the structural integrity of the transverse dunes is compromised, leading to an expansion in the size of the trail structures. Initially, the height of the dune surges, only to decline progressively over time, with the maximum fluctuation reaching nearly 1m. The height of larger dunes escalates gradually at first, peaks, and then subsides, with the pinnacle height nearing 6.5m. As a critical metric for safety evaluation, the height of the transmission line above ground initially plummets, then gradually rebounds, and shifts backward over time after hitting its nadir.

Investigating Role of Yarlung Zangbo River Valley as a Dust Source over the Tibetan Plateau, China

2025-06-24

Anqi Wang , Lanying Han , Zhibao Dong +3 more | Chinese Geographical Science

Shifting sands: Tracing the evolution of Prince Edward Island’s coastal dunes

2025-06-24

Barbara P. Rousseau | Coastal Studies & Society

Prince Edward Island (PEI) is the smallest Canadian province and only island province in Canada. This small sandstone island has a lengthy coastline, of which nearly one-third is classified as … Prince Edward Island (PEI) is the smallest Canadian province and only island province in Canada. This small sandstone island has a lengthy coastline, of which nearly one-third is classified as sand dune, and over half on the northern shore facing the long reach of the Gulf of St. Lawrence. While scientific interest has focused on coastal erosion, the role of coastal dunes is less understood, and historical records are scarce. However, the boundedness and small size of the island has historically provided opportunities for mapping, with the exacting surveys of Captain Samuel Holland in the eighteenth century, Admiral Henry Bayfield in the nineteenth century, and comprehensive aerial photo analysis and topographic mapping in the twentieth century. Overlaying these sources in a Geographic Information System (GIS), and comparing them with additional historical maps and charts at the site of the first settlement around St. Peters Bay provides insight into the rapid and continuing evolution of the nearby coastal sand dunes, which can in turn be linked to key eras in the island’s 300 years of colonial history.

Assessment of Wind-Related Parameters and Erodibility Potential Under Winter Wheat Canopy in Reclaimed Tidal Flat Land

2025-06-20

Kyo-Suk Lee , J.-H. Lee , Kwang-Seung Lee +4 more | Agronomy

The aim of this study was to observe soil erosion by wind, depending on the soil physical properties, climatic conditions, and plant canopy, for three representative soil series in the … The aim of this study was to observe soil erosion by wind, depending on the soil physical properties, climatic conditions, and plant canopy, for three representative soil series in the reclaimed tidal flats. Soil samples were collected from the Ap horizon of three soil series to analyze soil physical properties and particle distribution. Precipitation and wind velocities were measured by the weather station installed at the filed. The particle distribution curves showed that the actual proportions of erodible soil particle were in the order of 74.7%(TH), 66.1%(PS), and 62%(JB). The instantaneous and daily maximum wind speeds exceeded the threshold friction velocity (5.78 m s−1) suggested by Chepil. However, the dynamic velocities, depending on the radius of 0.125 mm and 0.42 mm belonging to erodible particle size, were much lower than the threshold friction velocity suggested by Chepil. The wind profile increases logarithmically with height, just above the plant canopy. The vertical gradients of wind velocity for the winter wheat plot were smaller than that of the bare plot due to the relatively rough canopy, and U(Z)c of the bare plot was slightly higher than that of the winter wheat plot with a plant canopy for the given U(Z)m. Conclusively, the actual proportion of erodible particles was much less than that of the particle size limit.

Analysis of microscopic motion and energy evolution of ballast particles by wind-blown sand penetration

2025-06-20

Yihao Chi , H. Xiao , Qiang Liu +4 more | Powder Technology

Research on the Distribution and Escape Characteristics of Dust at the Blasting Pile in an Open-Pit Mining Area

2025-06-20

Yong Cao , Xuefei Jiao , Rong Liu +5 more | Geosciences

In open-pit mines, substantial amounts of dust are generated at various stages. Due to the long duration, repeated mechanical disturbance, and large volume of material handled during the shoveling and … In open-pit mines, substantial amounts of dust are generated at various stages. Due to the long duration, repeated mechanical disturbance, and large volume of material handled during the shoveling and loading of blasting piles, this stage is recognized as one of the primary contributors to overall dust emissions in open-pit mining operations. The objective of this study is to investigate the spatial dispersion characteristics of dust at blasting piles and evaluate the influence of wind direction on dust migration and escape behavior. This study uses a full-scale numerical model to analyze the airflow and dust migration characteristics at blasting piles under different wind directions. Simulation results show that dust particles of different sizes exhibit distinct dispersion patterns: large particles settle near the source, medium particles migrate a moderate distance, and fine particles (PM2.5 and PM10) travel further and are more likely to escape from the pit. The leeward slope and pit bottom are identified as critical zones of dust accumulation and escape. Under both dump-side and stope-side wind conditions, respirable dust (d < 5 μm) accounts for more than 50% of the escaped particles, posing potential health risks to workers. These findings establish a scientific basis for targeted dust suppression strategies, supporting safer and more sustainable mine site management.

Coastal protection potential of natural dune systems threatened by SLR scenarios

2025-06-19

Björn Mehrtens , Oliver Lojek , Lukas Ahrenbeck +4 more | Research Square (Research Square)

<title>Abstract</title> Coastal dunes are key components of nature-based coastal protection, but they face increasing risk from sea-level rise driven by climate change. This study investigates the morphodynamic response of a … <title>Abstract</title> Coastal dunes are key components of nature-based coastal protection, but they face increasing risk from sea-level rise driven by climate change. This study investigates the morphodynamic response of a natural dune system at the German North Sea Coast to five storm surge cases with progressively rising still water levels (SWLs) reflecting local sea level rise (SLR) projections in 1:7 scaled experimental test series. Results reveal a systematic transition in flooding and erosion hazard regimes from localized, collision-induced dune retreat under current standard storm surge levels to major overwash and partial dune breaching under projected SLR projections of up to +1.2 m by 2100. Characteristic dune erosion processes of periodic scarping, notching, slumping, and sediment removal were found to migrate vertically with rising SWLs, progressively relocating the dune crest and increasing risk of breaching. In addition to the total dune erosion volume, the proportion of eroded area above SWL was identified as a sensitive indicator of residual dune protective capacity. The findings highlight the increasing vulnerability of natural dunes in the context of climate change-driven sea-level rise and underscore the urgent need for improved risk assessments and adaptive management strategies to preserve sufficient dune resilience and maintain their coastal protection function.

Numerical Simulation of Wind and Sand Resistance in Three Typical Shrubs

2025-06-13

Huimin Zhang , Liang Pei , Juyan Li +2 more | Sustainability

The sand-laden airflow fields surrounding Artemisia desertorum Spreng., Reaumuria soongorica, and Hedysarum scoparium were investigated. The study focuses on a configuration of double rows with staggered shrub distribution. Computational Fluid … The sand-laden airflow fields surrounding Artemisia desertorum Spreng., Reaumuria soongorica, and Hedysarum scoparium were investigated. The study focuses on a configuration of double rows with staggered shrub distribution. Computational Fluid Dynamics (CFD) simulations were employed to model the airflow. The resulting flow field was categorized into five distinct regions. The shelter distances downwind of the shrubs were observed to be 7 H, 6 H, and 6 H for A. desertorum, R. soongorica, and H. scoparium, respectively. The corresponding shelter widths were measured as 3 m, 3 m, and 8 m, respectively. The three kinds of shrubs all formed vortices behind the shrubs. Three shrub species demonstrated distinct wind shelter efficiency ranges: A. desertorum (0.5–4 H), R. soongorica (0.5–3 H), and H. scoparium (0.5–2 H). Optimal shelter effects were observed in different vertical layers: R. soongorica in the low (0–0.2 m), A. desertorum in the medium (0.2–0.7 m), and H. scoparium in the high (0.7–2.2 m) altitude layers. Overall, H. scoparium exhibited the highest sand resistance, followed by A. desertorum Spreng, with R. soongorica demonstrating the least resistance. This study offers theoretical insights for mitigating aeolian environmental degradation, particularly in safeguarding energy and transportation infrastructure in desert regions and promoting sustainable agricultural practices in arid areas.

Effects of the formation of shear-driven liquid-surface waves on the gas-phase turbulent boundary layer

2025-06-13

Nikolay Gustenyov , Sean Bailey | Experiments in Fluids

Fallowed Fields Are Fueling California’s Dust Problem

2025-06-13

Andrew R. Chapman | Eos

New research shows that unplanted agricultural lands are behind most of the state’s anthropogenic dust events. New research shows that unplanted agricultural lands are behind most of the state’s anthropogenic dust events.

Estimated epizoochory seed dispersal distances by grazing yak across seasons in an alpine meadow

2025-06-12

Shulin Wang , Fujiang Hou | Frontiers in Plant Science

Introduction Epizoochorous dispersal of grassland plants by large herbivores is an important way by which grassland plants achieve population expansion over long distances. However, little is known about the maximum … Introduction Epizoochorous dispersal of grassland plants by large herbivores is an important way by which grassland plants achieve population expansion over long distances. However, little is known about the maximum distance that seeds can be dispersed by domestic animals under seasonal grazing, which is the most common type of grassland management worldwide, especially in alpine regions. Methods To this end, we estimated the distance over which epizoochory dispersal occurs via yaks ( Poephagus grunniens ) for seven common plant species seeds in an alpine meadow under seasonal grazing using a simulated yak-fur seed adhesion test combined with observations of grazing behavior. Results The results showed that, as yak primary (e.g., walking time) and secondary (e.g., foraging rate) behavioral patterns differed significantly across seasons ( P &lt; 0.05), the epizoochory dispersal distances of plant seeds also had clear seasonal dynamics, manifesting as spring &gt; summer &gt; autumn &gt; winter, and that the length of seed adhesive structures correlated positively with the retention rate as well as retention time on yak fur. The relatively slow loss of diaspores observed in this study mainly shows that moving yak from one seasonal pasture to the following allows the dispersal of diaspores between two successive pastures. The dispersal scale was even wider (maximum dispersal distance of ~35 km) for seeds with special appendages (i.e., mucilage, sticking to the fur due to mucilage presence). Discussion Our results highlight that yaks are substantial seed dispersal vectors for alpine meadow plants and that seasonal grazing is a suitable management method for coping with habitat fragmentation as well as plant diversity conservation in alpine areas from the perspective of seed dispersal.

Tropical Central African bomb radiocarbon reveals antiphase air-mass atmospheric fluxes and vegetation-growth relationships

2025-06-12

Guaciara M. Santos , Lucas G. Pereira , Ana Carolina Maioli Campos Barbosa +4 more | The Science of The Total Environment

Where the Wind Wins: How Wind‐Eroded Patches Expand in Semi‐Arid Sandlands

2025-06-11

Shudong Zhang , Xuehua Ye , Guofang Liu +2 more | Bulletin of the Ecological Society of America

Controls on geomorphological stage of trough blowout evolution: Evidence from computational fluid dynamics (CFD) airflow modelling

2025-06-04

Duc Hau Nguyen , Sarah Wakes , Mike Hilton | Earth Surface Processes and Landforms

Abstract Trough blowouts are an important component of coastal dune systems since they facilitate sand transport from the beach to the backdune which can increase foredune width and resilience to … Abstract Trough blowouts are an important component of coastal dune systems since they facilitate sand transport from the beach to the backdune which can increase foredune width and resilience to erosion. The contemporary conceptual model of trough blowout evolution supposes that airflow acceleration over the deflation basin declines when the blowout reaches a critical cross‐section. To date, however, there is little evidence for this model. The current study examines how trough blowout morphology ‐ including the slope of the bed surface (from 10° to 25°), the slope of lateral walls (from 60° to 90°) and trough width (from 10 to 50 m), controls airflow dynamics and shear velocity during various incident wind speeds and directions. Computational Fluid Dynamics (CFD) is used to model flow where the incident wind angle varies from 0° to 80° relative to the long axis of the blowout. The results support the contemporary conceptual model. Increasing bed slope, decreasing wall slope and increasing blowout width result in a decrease in average shear velocity on the lateral walls and bed surface of the blowout. We also found that measurements of wind speed at the middle of the blowout might not be sufficient to predict trough blowout evolution in oblique incident wind conditions because of the occurrence of helicoidal flow inside the blowout, which results in a complex erosion pattern on the lateral walls and bed surface. We also found a strong linear relationship between the shear velocity of incident winds and the average shear velocity on the lateral walls and bed surface of the blowout. This relationship could assist coastal managers to select locations where the incident wind speed is strong enough to maintain artificial trough blowouts to address coastal problems.

Aerodynamic roughness of rippled beds under active saltation at Earth-to-Mars atmospheric pressures

2025-06-02

Carlos A. Alvarez , M. G. A. Lapôtre , Christy Swann +3 more | Nature Communications

As winds blow over sand, grains are mobilized and reorganized into bedforms such as ripples and dunes. In turn, sand transport and bedforms affect the winds themselves. These complex interactions … As winds blow over sand, grains are mobilized and reorganized into bedforms such as ripples and dunes. In turn, sand transport and bedforms affect the winds themselves. These complex interactions between winds and sediment render modeling of windswept landscapes challenging. A critical parameter in such models is the aerodynamic roughness length, z0, defined as the height above the bed at which wind velocity predicted from the log law drops to zero. In aeolian environments, z0 can variably be controlled by the laminar viscous sublayer, grain roughness, form drag from bedforms, or the saltation layer. Estimates of z0 are used on Mars, notably, to predict wind speeds, sand fluxes, and global circulation patterns; yet, no robust measurements of z0 have been performed over rippled sand on Mars to date. Here, we measure z0 over equilibrated rippled sand beds with active saltation under atmospheric pressures intermediate between those of Earth and Mars. Extrapolated to Mars, our results suggest that z0 over rippled beds and under active saltation may be dominated by form drag across a plausible range of wind velocities, reaching values up to 1 cm-two orders of magnitude larger than typically assumed for flat beds under similar sediment transport conditions.

Direct Interception of Particles by a Vegetation Stem With Varying Adhesive Forces

2025-06-01

Mahdi Khademishamami , Lawrence P. Sanford , William Nardin +1 more | Journal of Geophysical Research Earth Surface

Abstract The direct interception of particles by vegetation stems has been reported in field studies of saltmarsh platforms as a major cause for removing suspended particles and pollutants. Laboratory observations … Abstract The direct interception of particles by vegetation stems has been reported in field studies of saltmarsh platforms as a major cause for removing suspended particles and pollutants. Laboratory observations and numerical models reported in the literature have computed the attachment efficiency under the assumption that particles stick and do not move when they collide with the surface of the collector (i.e., perfect attachment). This study was aimed at lifting this assumption using a Discrete Element Model (DEM) with varying adhesive contact forces coupled with Computational Fluid Dynamics (CFD). The CFD‐DEM model considers the stickiness of the collector through a surface energy parameter. Model predictions showed good agreement with laboratory observations. The final configuration of particles on the collector's surface and the attachment efficiency changed when the collector's surface energy was varied. In some cases, the attachment efficiency was twice that under the perfect attachment assumption, indicating that modeling studies with perfect attachment may underestimate suspended particle removal. As biofilms are considered the main cause of the adhesiveness of stems, our study shows that any biofilm formation that could create a surface energy as low as 0.01 could lead to attachment of particles on a single saltmarsh stem.

Editorial preface to special issue: Variability and driving mechanisms of Asian dust storms from the Holocene to the present

2025-06-01

Jianbao Liu , Mingrui Qiang , Shugang Kang +1 more | Global and Planetary Change

Seasonal Variability Observed in the Gulf Stream East of Cape Hatteras

2025-06-01

Adrienne Silver , Avijit Gangopadhyay , Magdalena Andres +1 more | Journal of Geophysical Research Oceans

Abstract The Gulf Stream system is dominated by strong mesoscale variability that can obscure any seasonal signals in Gulf Stream strength. Nevertheless, seasonal variability of the Gulf Stream is important … Abstract The Gulf Stream system is dominated by strong mesoscale variability that can obscure any seasonal signals in Gulf Stream strength. Nevertheless, seasonal variability of the Gulf Stream is important for local weather and climate and can influence amplification of hurricane intensity and storm tracks. We investigate seasonal variability of the speed of the Gulf Stream after it detaches from Cape Hatteras, using high‐resolution along‐track altimeter data. The altimeter data show a significant seasonal cycle in the Gulf Stream axis speed, peaking in summer. The seasonal variability in the Gulf Stream axis velocity is related to changes in the local wind stress curl and changes in the density difference across the Gulf Stream. Wind forcing affects the Gulf Stream year‐round, while changes in the density difference have the largest impact in summer. Overall, changes in the wind stress curl and upper ocean density difference across the Gulf Stream can explain roughly 40% of the seasonal Gulf Stream speed variability in summer.

Numerical modelling of airflow and sediment transport patterns over Aeolian coastal sand dunes: Effects of dune slope and wind direction

2025-06-01

Paran Pourteimouri , Abraham Jonkheer , Gerhardus Hermanus Petrus Campmans +1 more | Geomorphology

Effect of aerial biostimulant applications to reduce abiotic stress conditions

2025-06-01

Rodrigo Assar , L. Ahumada-Orellana , C. Abud +2 more | Acta Horticulturae

Properties, challenges, and opportunities of the loess plains in the northern Negev Desert: A review

2025-06-01

Ilan Stavi , G. L. Kagan , Sivan Isaacson | Journal of Arid Land

Geomorphology of mega-dunes in the eastern Taklimakan Desert

2025-06-01

Hao Li , Xin Gao , Yongcheng Zhao +3 more | Journal of Geographical Sciences

The diversity of biological models for bio-inspired aerosol filters

2025-06-01

Leandra Hamann , Timothy G. Foat , Alexander Blanke | Journal of The Royal Society Interface

Innovative filtration systems are essential to enhance air quality or improve aerosol sampling for analysis, while addressing challenges such as high energy consumption, clogging and inefficiencies in capturing a wide … Innovative filtration systems are essential to enhance air quality or improve aerosol sampling for analysis, while addressing challenges such as high energy consumption, clogging and inefficiencies in capturing a wide range of particle diameters. Bio-inspiration provides novel design strategies by translating natural particle separation mechanisms (PSMs) into more efficient, adaptive and sustainable filtration technologies. This review systematically identifies six organismic groups as biological models that use distinct particle capture mechanisms to retain airborne particles for nutrition, reproduction and protection. Filtration-based PSMs in air, such as insect spiracles, hornet silk caps and spider webs, employ dead-end filtration with varying mesh structures to either purify air or capture prey. Non-filtration PSMs, including nasal cavities and wind pollination, rely on passive aerodynamic mechanisms such as impaction, interception and settling for particle retention. Flow regime control is crucial for non-filtration PSMs, where structures like nasal turbinates and pine cone surfaces optimize local airflows. Adhesive mechanisms, found in spider webs and nasal mucus, improve particle attachment. By mapping these principles to aerosol filtration challenges—such as particle adhesion, flow optimization and efficient removal of submicrometre particles—this review identifies promising pathways for bio-inspired aerosol filters in environmental monitoring, industrial hygiene and public health.

Barchans Interacting With Dune‐Size Obstacles: Details of the Fluid Flow and Motion of Grains

2025-06-01

Nicolao Cerqueira Lima , Willian Righi Assis , Danilo S. Borges +1 more | Journal of Geophysical Research Earth Surface

Abstract We investigate details of the interaction of subaqueous barchans with dune‐size obstacles by carrying out numerical simulations where the fluid is solved at the grain scale and the motions … Abstract We investigate details of the interaction of subaqueous barchans with dune‐size obstacles by carrying out numerical simulations where the fluid is solved at the grain scale and the motions of individual grains are computed at all time steps. With the outputs, we analyze the disturbances of the fluid flow, the trajectories of grains, and the resultant force on each grain, the latter being unfeasible from experiments and field measurements. We show that in some cases particles pass over the obstacle, while in others they completely circumvent it (without touching it), or are even blocked. For the circumvention and blocking cases, which we call bypass and trapped, respectively, we show the existence of a strong vortex between the lee face of the dune and the obstacle. This vortex results from the interactions of recirculation regions and horseshoe vortices, and has enough strength to deviate the main flow and carry grains around the obstacle in those cases. Our results shed light on the reasons for passing over, circumventing, and blocking, and contribute to our understanding of dunes in the presence of large obstacles such as hills, crater rims, and human constructions.

Quantification of Particle Velocities and Energy Regime in an Aeolian Abrasion Chamber

2025-06-01

Joanna E. Bullard , Lucrecia Alvarez‐Barrantes , Cheryl McKenna Neuman +1 more | Journal of Geophysical Research Earth Surface

Abstract Particle breakdown and fine sediment production by wind abrasion is of long‐standing interest in aeolian science as it contributes to erosion and dust production on Earth and other planetary … Abstract Particle breakdown and fine sediment production by wind abrasion is of long‐standing interest in aeolian science as it contributes to erosion and dust production on Earth and other planetary bodies. The process of aeolian abrasion is largely measured in laboratories to enable standardization of parameters and allow simulation of saltation over long time periods. To be effective, abrasion simulators must reproduce particle interactions similar to those observed in the natural environment. This paper quantifies the particle velocities, pathways and energy regime within a widely used “test‐tube” abrasion chamber. For 17 different sand samples, the instantaneous two‐dimensional vertical and horizontal velocity components of particles moving within the chamber were sampled using a laser Doppler anemometer. Similar to a natural saltation cloud, the movement of particles in the chamber is stochastic and there is a positive relationship between the air inflow rate and the depth of the saltation layer. For air inflow of 14.9 m s −1 , particle velocities range from 0.01 to 3.2 m s −1 with median velocity for all particles in the chamber varying from 0.29 to 0.56 m s −1 , and total energy ranging from 0.54 to 1.38 J kg −1 . These values are similar to those determined for natural saltation clouds. For a constant air inflow rate, the mean total particle velocity increases with particle size. Air inflow rate has a significant effect on mean total particle velocity but between 10 and 100 g the quantity of sample tested is not important. The contribution of this type of experiment to understanding aeolian abrasion processes is evaluated.