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1.
GPR provides high resolution images of aeolian strata in frozen sand in the McMurdo Dry Valleys of Antarctica. The results have positive implications for potential GPR surveys of aeolian strata on Mars. Within the Lower Victoria Valley, seasonal changes in climate and a topographically-constrained wind regime result in significant wind reversals. As a consequence, dunes show reversing crest-lines and flattened dune crests. Ground-penetrating radar (GPR) surveys of the dunes reveal sets of cross-strata and low-angle bounding surfaces produced by reversing winds. Summer sand transport appears to be dominant and this is attributed to the seasonal increase in solar radiation. Solar radiation which heats the valley floor melts ice cements making sand available for transport. At the same time, solar heating of the valley floor generates easterly winds that transport the sand, contributing to the resultant westward dune migration. The location of the dune field along the northern edge of the Lower Victoria Valley provides some shelter from the powerful föehn and katabatic winds that sweep down the valley. Topographic steering of the winds along the valley and drag against the valley wall has probably aided the formation, migration and preservation of the dune field. Optically-stimulated luminescence (OSL) ages from dune deposits range from 0 to 1.3 kyr showing that the dune field has been present for at least 1000 yr. The OSL ages are used to calculate end-point migration rates of 0.05 to 1.3 m/yr, which are lower than migration rates reported from recent surveys of the Packard dunes and lower than similar-sized dunes in low-latitude deserts. The relatively low rates of migration are attributed to a combination of dune crest reversal under a bimodal wind regime and ice cement that reduces dune deflation and restricts sand entrainment.  相似文献   

2.
Sunset Crater in north‐central Arizona (USA) is a 900‐year‐old scoria‐cone volcano. Wind action has redistributed its widespread tephra deposit into a variety of aeolian dune forms that serve as a terrestrial analog for similar landforms and aeolian processes on Mars. Fieldwork was conducted to collect essential geomorphological and sedimentological data, and to establish a baseline for the type and morphometry of dunes, physical properties, interactions with topography, and saltation pathways. Our analyses focused primarily on coppice dunes, falling dunes, wind ripples, and sand streaks. For all collected volcaniclastic aeolian sediment samples, the sand‐size fraction dominated, ranging from almost 100% sand to 74.6% sand. No sample contained more than 1.6% silt. The composition is overwhelmingly basaltic with non‐basaltic particles composing 2 to 6% of the total. Coppice (nebkha) dunes form where clumps of vegetation trap saltating particles and create small mounds or hummocks. Mean grain size for coppice dune samples is coarse sand. Measured dune height for 15 coppice dunes ranged from 0.3 to 3.3 m with a mean of 1 m. Mean length was 6.7 m and mean width was 4.8 m. Falling dunes identified in this study are poorly developed and thin, lacking a prominent ramp‐like structure. Mean wavelength for three sets of measured ripples ranged from 22 to 36 cm. Sand streaks extend downwind for more than a kilometer and are up to 200 m in width. They commonly occur on the lee side of mesas and similar landforms and are typically the downwind continuation of falling dunes. Falling dunes, wind ripples, and sand streaks have been identified on Mars, while coppice dunes are similar to Martian shadow or lee dunes in which sand accumulates in the lee of obstacles. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

3.
The Hulunbuir dune field (HLB) is situated near the northern limit of the East Asian summer monsoon (EASM), and vulnerable to climate change. The aeolian sand–paleosol sequences of this region are crucial for understanding the past landform processes in response to climate change, but not yet understood well due to chronological controversies. Here, we presented 20 optically stimulated luminescence (OSL) ages from five aeolian sand–paleosol profiles in the HLB, and reconstructed the aeolian landform processes since 18 ka. The findings of this study suggested that the HLB was probably dominated by mobile dunes before 18 ka, as 10 out of 11 aeolian samples were dated to 18–12 ka. Two strong sandy paleosol layers were found and dated to ∼9 ka and 5–0.5 ka, indicating that strong in situ pedogenic process on the accumulative sand could occur during the Holocene. The OSL ages of samples near the top of three profiles were >9.5 ka, indicating two possible surface processes. First, the land surface was stable since 9.5 ka after stabilization, with no accumulation or erosion. Alternatively, the surface could have been erosive with the eroded sediments feeding downwind active dunes. The latter explanation is consistent with the current local landforms, which has widespread blowout pits, indicators of strong wind erosion. We emphasized that the OSL age of a sand layer sample in fossil dunes implied the onset of mobile dune stabilization, not the age of dune activity, as previously stated.  相似文献   

4.
Basically, sand dunes are patterns resulting from the coupling of hydrodynamic and sediment transport. Once grains move, they modify the surface topography which in turns modifies the flow. This important feedback mechanism lies at the core of continuous dune modelling. Here we present an updated review of such a model for aeolian dunes, including important modifications to improve its predicting power. For instance, we add a more realistic wind model and provide a self‐consistent set of parameters independently validated. As an example, we are able to simulate realistic barchan dunes, which are the basic solution of the model in the condition of unidirectional flow and scarce sediments. From the simulation, we extract new relations describing the morphology and dynamics of barchans that compare very well with existing field data. Next, we revisit the problem of the stability of barchan dunes and argue that they are intrinsically unstable bed‐forms. Finally, we perform more complex simulations: first, a barchan dune under variable wind strength and, second, barchan dune fields under different boundary conditions. The latter has important implications for the problem of the genesis of barchan dunes. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

5.
Reticulate dunes are one of the commonest dune types, and yet the least understood. Reticulate dunes at southeastern Tengger Desert are constituted by NE-SW trending primary ridges and nearly vertical secondary ridges. The result of field work studying the morphodynamics and formation mechanism for reticulate dunes in this area shows that the primary ridges were formed by dominant northwest wind and the secondary ridges developed and maintained by alternating dominant wind and subdominant northeast wind on the basis of the primary ridges. Viewed from morphodynamics, reticulate dunes correspond to the complex transverse dune on which the longitudinal element superimposed. Project supported by the National Natural Science Foundation of China (Grant No. NSFC-49501001).  相似文献   

6.
The southwestern Kalahari linear dunefield, which displays marked morphological variability, possesses a partial but temporally and spatially variable vegetation cover and has frequently been described as a palaeodunefield. Palaeo status has been ascribed on the basis of several criteria including the presence of vegetation, but also because dunes are thought to be out of alignment with modern resultant potential sand-moving wind directions and because present-day wind energy is regarded as low. For the period 1960–1992, wind data from eight dunefield meteorological stations are analysed in detail to examine these assertions. Potential sand transport directions, including spatial and temporal variations, and potential drift directions for the windiest three month periods, are calculated and explained. It is concluded that the present-day potential sand transport environment is markedly variable from year to year and from place to place. While periods of low sand transport energy do occur, it is also noted that the 1980s possessed considerable potential for sand transport in the dunefield. Directional variability is also relatively high, perhaps exceeding that under which linear dunes can be expected to form. Because linear dune aeolian activity has a number of states, however, the present-day wind environment may allow dune surface aeolian activity to occur which does not alter the overall pattern of the dunes.  相似文献   

7.
A relatively unknown coastal zone of southern Mozambique in Africa is covered by vast mobile and stabilized dunefields. The aeolian dynamics of these transgressive dunefields are studied based on mobility and stability models, statistical analysis of climate data and topographic profiles. Detailed analyses of regional winds, rainfall records, atmospheric temperature records and annual monitoring of dune migration rates helped to find reliable data about instantaneous aeolian sand transport rates, wind drift potential, dune mobility and dune migration rates. The data obtained suggest that the coastal transgressive dunefields are controlled by the southeast winds, availability of loose sediments on the beach, the presence of headland boundary between Maputo and Gaza provinces and the appropriate deposition spaces between the coastline and lacustrine‐lagoon systems. Two distinctive segments of transgressive dunefields were identified in the region studied, including the northern segment of Maputo province with active (mobile) and semi‐vegetated dunes that migrate 23 m/yr landward, and Gaza province dunefields with stabilized (vegetated) and semi‐vegetated dunes. The data obtained in this research have considerable potential to make a valuable contribution to the study of coastal dunefields. Copyright © 2018 John Wiley & Sons, Ltd.  相似文献   

8.
Lateral migration of linear dunes in the Strzelecki desert,Australia   总被引：1，自引：0，他引：1  
Linear dunes in the Strzelecki Desert trend roughly south-north. Sand transport, which is toward the NNE, has caused the dunes to migrate eastward while they extend or migrate northward. Eastward lateral migration is evidenced by: (1) asymmetrical shape of the dunes; east-facing slopes are several times as steep as west-facing slopes; (2) asymmetrical accumulation of loose recently transported sand (relatively abundant on east-facing slopes); (3) asymmetrical outcropping of older semiconsolidated aeolian sand on the dune surface (more abundant on west-facing slopes); and (4) east-dipping foreset beds that underly the west-facing flanks of some dunes. Dunes in the Strzelecki Desert are still active in the sense that sand is transported along and across many dune crests. However, the dunes are composed primarily of Pleistocene strata, indicating that the trend of the dunes was established before the Holocene. The obliquity of the dunes to the transport direction is not merely an aberration of the wind regime of the last few decades. Preferential accumulation of sand on east-facing flanks indicates that the dunes migrated eastward several metres during the Holocene. Moreover, the west-facing flanks of some dunes have experienced a minimum of tens of metres of erosion. This asymmetric erosion and deposition were caused by dune obliquity and lateral migration that may have begun as early as the Pleistocene. Dunes in the Strzelecki Desert and in the adjacent Simpson Desert display a variety of grossly different internal structures. Computer graphics experiments demonstrate that many of these differences in structure can be explained by different angles of climb of the dunes.  相似文献   

9.
Sand dunes as potential sources of dust in northern China   总被引：1，自引：0，他引：1  
While saltation bombardment of sand grains on a fine substrate can produce considerable dust, the well-sorted nature of sand dunes tends to preclude them from consideration as major dust sources. Recent research, however, has revealed that sand dunes can, in some cases, be large sources of dust. We used the PI-SWERL(Portable In-Situ Wind Erosion Laboratory) to measure in the field the potential of sand dunes and other desert landforms to emit particulate matter 10 μm(PM-10) dust in the Tengger, Ulan Buh, and Mu Us deserts of northern China. Combined with high resolution particle size measurements of the dune sand, an assessment of sand dunes as a dust source can be made. Large active transverse dunes tend to contain little to no stored PM-10, yet they produce a low dust flux. Coppice dunes stabilized by vegetation contain appreciable PM-10 and have very high dust emission potential. There is a positive correlation between the amount of PM-10 stored in a dune and its potential dust flux. Saltation liberates loose fines stored in dunes, making them very efficient dust emitters compared to landforms such as dry lake beds and washes where dust particles are unavailable for aeolian transport due to protective crusts or sediment cohesion. In cases where large dunes do not store PM-10 yet emit dust when active, two hypotheses can be considered:(1) iron-oxide grain coatings are removed during saltation, creating dust, and(2) sand grains collide during saltation, abrading grains to create dust. Observations reveal that iron oxide coatings are present on some dune sands. PI-SWERL data suggests that low dust fluxes from dunes containing no stored dust may represent an estimate for the amount of PM-10 dust produced by removal of iron oxide coatings. These results are similar to results from dunes in the United States. In addition, PI-SWERL results suggest that dust-bearing coppice dunes, which cover vast areas of China's sandy deserts, may become major sources of dust in the future if overgrazing, depletion of groundwater, or drought destabilizes the vegetation that now partially covers these dunes.  相似文献   

10.
An association between salt pans or dry lake beds and distinctive crescentic lake-floor sand mounds (1–10 m high, tens to hundreds of metres wide) is commonplace in desert systems. In the Makgadikgadi Basin of northern Botswana, a debate about the formative processes of these landforms has persisted despite numerous morphometric, sedimentary and geochronological analyses, with mound landforms variously inferred to be aeolian dunes, subaqueous dunes, spring mounds or shoreline remnants. We propose a new formative mechanism which draws on the interaction between uneven moisture distribution on the pan surface and mobile aeolian sediments. We use a numerical model (ViSTA), which couples vegetation and aeolian sand transport dynamics, together with optically stimulated luminescence (OSL) dating of a mound in the Makgadikgadi Basin to investigate the feasibility of this ‘sticky mound hypothesis’. We find that under a range of modelled environmental conditions, uneven moisture distribution on the pan surface can lead to the development and stabilization of crescentic aeolian dunes, with these dunes growing upwind from the point of initial deposition, corresponding with the chronological data gained from OSL dating of a mound feature. On removal of this moisture, the modelled dunes erode and dissipate. These findings suggest that the formative mechanism of the mounds could be dependent on the interaction between differential drying of the pan surface and the competence of the aeolian sediment transport system across the pan floor.  相似文献   

11.
The eastern portion of the Maranhão coast is characterized by large active dune‐fields located in a tropical setting. This article combines the analysis of dune‐field morphologic patterns with the classical analysis of grain size and heavy minerals to study the sedimentary dynamics of the active aeolian system in this region. Based on the heavy mineral analysis, the main sedimentary suppliers feeding the system are the westward alongshore drift bringing sand from the coast east of the Parnaíba River mouth and the river itself. The absence of well‐defined variation patterns of the two morphometric parameters studied, dune spacing and crest length, reflects complex sedimentary dynamics and transport pathways, inside the aeolian system, despite the unidirectional wind. During the wet season, the interdune plains are flooded and the system is intensely reworked by intermittent drainages. During the dry season, the deposits formed by the drainages and interdune lakes become temporary internal sedimentary sources for the system. Due to this combined aeolian‐fluvial transport, the sediment source area has a planar geometry, with contributions from the beach and interdune plains, and not linear as expected in a typical case of source only in the beach. The areal limits of the dune‐fields is the main boundary condition controlling the dune‐field patterns, as dune spacing and crest length, by changing the sedimentary inflow–outflow balance and interactions between migration dunes. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

12.
This paper discusses a two-dimensional second-order closure model simulating air flow and turbulence across transverse dunes. Input parameters are upwind wind speed, topography of the dune ridge and surface roughness distribution over the ridge. The most important output is the distribution of the friction velocity over the surface. This model is dynamically linked to a model that calculates sand transport rates and the resulting changes in elevation. The sand transport model is discussed in a separate paper. The simulated wind speeds resemble patterns observed during field experiments. Despite the increased wind speed over the crest, the friction velocity at the crest of a bare dune is reduced compared to the upstream value, because of the effect of stream line curvature on turbulence. These curvature effects explain why desert dunes can grow in height. In order to obtain realistic predictions of friction velocity it was essential to include equations for the turbulent variables in the model. In these equations streamline curvature is an important parameter. The main flaw of the model is that it cannot deal with flow separation and the resulting recirculation vortex. As a result, the increase of the wind speed and friction velocity after a steep dune or a slipface will be too close to the dune foot. In the sand transport model this was overcome by defining a separation zone. Copyright © 1999 John Wiley & Sons, Ltd.  相似文献   

13.
The evolution of barchan-to-parabolic dunes can be driven by vegetation establishment, which may be linked to climate change and/or human activity. However, little is known of the impact of changes in wind strength on vegetation development and the resulting impacts on the evolution of dune morphology and sedimentological characteristics. To address this issue, we studied the morphology and grain-size characteristics of barchan, barchan-to-parabolic and parabolic dunes in the Mu Us Desert in north China, which was combined with an analysis of changes in normalized difference vegetation index (NDVI) and climatic variables during 1982–2018. The results reveal a trend of increasing growing-season NDVI which was related to a significant decrease in drift potential (DP). Therefore, we suggest that the initiation of dune transformation was caused by the reduced wind strength which favored the establishment and development of vegetation. To reveal the response of sedimentological reorganization during the processes of dune transformation, grain-size characteristics along the longitudinal profile of the three different types of dunes were examined. The decreasing wind strength led to the transport of fine sands on the upper part of the windward face of the dunes, resulting in a progressive coarsening of the grain-size distribution (GSD) and a reduction in dune height at the crest area. No distinct trend in sorting and mean grain-size was observed on the windward slope of the barchan-to-parabolic dune, indicating that the sand in transit had little influence on the GSD. Conversely, progressive sorting and coarsening of the sand occurred towards the crest of the parabolic dune. This indicates that vegetation development limited the transport of sand from upwind of the dune, and affected a shift in the dune source material to the underlying source deposits, or to reworked pre-existing aeolian deposits, and resulted in the trapping of sand in the crest area. © 2020 John Wiley & Sons, Ltd.  相似文献   

14.
A cellular automata model is used to analyze the effects of groundwater levels and sediment supply on aeolian dune development occurring on sand flats close to inlets. The model considers, in a schematized and probabilistic way, aeolian transport processes, groundwater influence, vegetation development, and combined effects of waves and tides that can both erode and accrete the sand flat. Next to three idealized cases, a sand flat adjoining the barrier island of Texel, the Netherlands, was chosen as a case study. Elevation data from 18 annual LIDAR surveys was used to characterize sand flat and dune development. Additionally, a field survey was carried out to map the spatial variation in capillary fringe depth across the sand flat. Results show that for high groundwater situations, sediment supply became limited inducing formation of Coppice-like dunes, even though aeolian losses were regularly replenished by marine import during sand flat flooding. Long dune rows developed for high sediment supply scenarios which occurred for deep groundwater levels. Furthermore, a threshold depth appears to exist at which the groundwater level starts to affect dune development on the inlet sand flat. The threshold can vary spatially depending on external conditions such as topography. On sand flats close to inlets, groundwater is capable of introducing spatial variability in dune growth, which is consistent with dune development patterns found on the Texel sand flat.  相似文献   

15.
The introduction of vegetation to bare barchan dunes can result in a morphological transformation to vegetated parabolic dunes. Models can mimic this planform inversion, but little is known about the specific processes and mechanisms responsible. Here we outline a minimalist, quantitative, and process‐based hypothesis to explain the barchan–parabolic transformation. The process is described in terms of variations in the stabilization of wind‐parallel cross‐sectional dune slices. We hypothesize that stabilization of individual ‘dune slices’ is the predictable result of feedbacks initiated from colonization of vegetation on the slipface, which can only occur when slipface deposition rates are less than the deposition tolerance of vegetation. Under a constant vegetation growth regime the transformation of a barchan dune into a parabolic dune is a geometric response to spanwise gradients in deposition rates. Initial vegetation colonization of barchan horns causes shear between the anchored sides and the advancing centre of the dune, which rotates the planform brinkline angle from concave‐ to convex‐downwind. This reduces slipface deposition rate and allows vegetation to expand inward from the arms to the dune centre. The planform inversion of bare barchans dunes into vegetated parabolic dunes ultimately leads to complete stabilization. Our hypothesis raises several important questions for future study: (i) are parabolic dunes transitional landforms between active and vegetation‐stabilized dune states? (ii) should stabilization modelling of parabolic dune fields be treated differently than linear dunes? and (iii) are stabilized parabolic dune fields ‘armoured’ against re‐activation? Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

16.
The dune system in Otindag sand field of northern China is sensitive to climate change, where effective moisture and related vegetation cover play a controlling role for dune activity and stability. Therefore, aeolian deposits may be an archive of past environmental changes, possibly at the millennial scale, but previous studies on this topic have rarely been reported. In this study, thirty-five optically stimulated luminescence (OSL) ages of ten representative sand-paleosol profiles in Otindag sand field are ob-tained, and these ages provide a relatively complete and well-dated chronology for wet and dry varia-tions in Holocene. The results indicate that widespread dune mobilization occurred from 9.9 to 8.2 ka, suggesting a dry early Holocene climate. The dunes were mainly stabilized between 8.0 and 2.7 ka, implying a relatively wet climate, although there were short-term penetrations of dune activity during this wet period. After ~2.3 ka, the region became dry again, as inferred from widespread dune activity. The "8.2 ka" cold event and the Little Ice Age climatic deterioration are detected on the basis of the dune records and OSL ages. During the Medieval Warm Period and the Sui-Tang Warm Period (570-770 AD), climate in Otindag sand field was relatively humid and the vegetation was denser, and the sand dunes were stabilized again. These aeolian records may indicate climate changes at millennial time scale during Holocene, and these climatic changes may be the teleconnection to the climate changes elsewhere in the world.  相似文献   

17.
The formation of the complex linear dunes in the central Taklimakan Sand Sea is discussed based on analyses of wind regimes, sand grain size distributions on the topography of the dunes, and a combination of geomorphic and geophysical investigations into the morphology of the dunes. Complex linear dune formation is shown to have ?ve stages. Analysis clearly shows that under the control of wind regime, sand supply and other factors, the simple linear dunes move sideways while they evolve. This is the main cause for the formation of complex linear dunes in the central Taklimakan Sand Sea. We have not collected enough evidence to show whether the complexity of the complex linear dunes is left over from previous wind regimes or whether the previous wind regimes had different dominant wind directions compared to those of modern winds. The evolutionary processes of complex linear dunes in the region partly support the theory of ‘barchan evolution’ but do not support the ‘roll‐vortex’ and ‘bimodal wind regime’ hypotheses. After the complex linear dunes were developed, the local wind regime and the other controls such as sand supply suggest it is possible for them to maintain their linear shape. The evolutionary process discussed is limited to the region indicated in this paper, and may not be applicable to the whole Taklimakan Sand Sea. There are different evolutionary processes in different dune?elds because of variations in the factors that control complex linear dune formation. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   

18.
Sedimentary architecture and genesis of residual dune ridges in a temperate climate are presented and implications for their use as archive of changes in long-term precipitation and wind climate are discussed. Residual dunes are common features of wet aeolian systems, where they form sets of shallow ridges, oriented perpendicular to the prevailing wind direction. Residual dune ridges of the study area are vegetated and typically elevate 0.6 to 2.5 m above the surrounding interdune flats. They develop on the lower stoss side of active transgressive dunes, triggered by periods of elevated groundwater table and hence colonization of the foot of the dune by rapid growing pioneer vegetation. Stabilized by plants, the growing ridge detaches from the active transgressive dune and gets abandoned within years in the course of the downwind-migration of the transgressive dune. Grain-size data suggest a main sediment supply from the transgressive dune and only minor input from other sources. Ground-penetrating radar reveals that the residual dune ridges are composed of windward-dipping as well as leeward-dipping sedimentary beds. Leeward-dipping strata reflect sediment supply from the parental dune, whereas windward-dipping beds are seen to result from sediment redistribution along the ridge and sediment supply from the adjacent swales during the ridge growth period. Multi-annual to multi-decadal variability in precipitation leads to the development of sequences composed of tens of ridges, spanning time periods of several centuries. Spacing of individual ridges in these sequences is controlled not by long-term variability in precipitation alone, but probably also reflects variable wind intensity which affects the migration rate of the parental dune. The important role of vegetation in ridge construction makes these landforms a demonstrative example of landscape development by geo-biosphere interacting processes.  相似文献   

19.
In this work, we perform an analysis of large dark dunes within Moreux Crater and Herschel Crater on Mars using High Resolution Imaging Science Experiment (HiRISE) and Context Camera (CTX) data sets. These data allow us to conduct a detailed analysis of dune morphology and slip faces, concluding that the studied dune fields are influenced by topographically‐controlled complex wind directions. Our morphological analysis reveals that inside Moreux Crater in particular, the topographic setting dominates the wind flow direction, leading to the development of a sand transport pathway encircling the central peak of the crater. The dune fields in Herschel Crater are also affected by winds controlled by variable topography as suggested by the presence of complex dunes and dune fields. Our analysis indicate that the studied dune systems is not the result of paleo‐wind regimes. Furthermore, we perform thermal inertia measurements using thermal emission spectrometer (TES) data, which indicate that the studied dune fields consist of medium sand 250–500 µm in diameter. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

20.
A computer simulation model for transverse‐dune‐field dynamics, corresponding to a uni‐directional wind regime, is developed. In a previous formulation, two distinct problems were found regarding the cross‐sectional dune shape, namely the erosion in the lee of dunes and the steepness of the windward slopes. The first problem is solved by introducing no erosion in shadow zones. The second issue is overcome by introducing a wind speedup (shear velocity increase) factor, which can be accounted for by adding a term to the original transport length, which is proportional to the surface height. By incorporating these features we are able to model dunes whose individual shape and collective patterns are similar to those observed in nature. Moreover we show how the introduction of a non‐linear shear‐velocity‐increase term leads to the reduction of dune height, and this may result in an equilibrium dune field configuration. This is thought to be because the non‐linear increase of the transport length makes the sand trapping efficiency lower than unity, even for higher dunes, so that the incoming and the outgoing sand flux are in balance. To fully describe the inter‐dune morphology more precise dynamics in the lee of the dune must be incorporated. Copyright © 2000 John Wiley & Sons, Ltd.  相似文献   

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