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Through a field experiment on a sandy beach at Pingtan, China, we propose the first model to characterize the variability of apparent von Kármán parameter κa ${\kappa }_{a}$ in the thermally and sedimentologically stratified air flows. The model shows that κa ${\kappa }_{a}$ is negatively correlated to flux Richardson number as well as sediment transport rate. The atmospheric stability can be either from thermal stratification or sedimentological stratification, neglecting either of them can lead to substantial errors in predicting shear velocity and sediment transport rate. Plain Language Summary: In natural conditions, atmospheric boundary layer flows are often non‐neutral due to thermal stratification. However, recent studies indicate sedimentological stratification may also have a similar effect while almost no research was conducted to examine their combined effect on the flows. We present the first model to characterize the apparent von Kármán parameter κa ${\kappa }_{a}$, a parameter representing the scale of flow eddy size, as a function of thermal and sedimentological stabilities. This work provides a feasible means to correct the potentially substantial errors when estimating shear velocity and predicting sediment transport rate for sedimentologically and thermally stratified air flows. Key Points: Apparent von Kármán parameter for thermally and sedimentologically stratified air flows was obtainedApparent von Kármán parameter has a negative, linear relationship with flux Richardson number and sediment transport rateNeglecting thermal and sedimentological stratifications can lead to substantial errors in shear velocity and transport rate estimations [ABSTRACT FROM AUTHOR]

ABSTRACT Sediment distribution is investigated applying grain size analysis to 279 surface samples from the transitional zone between high mountains (Qilian Shan) and their arid forelands (Hexi Corridor) in north-western China. Six main sediment types were classified. Medium scale (103 m) geomorphological setting is carefully considered as it may play an important role concerning sediment supply and availability. A tripartite distribution of sedimentological landscape units along the mountain to foreland transition is evident. Aeolian sediments (e.g. loess and dune sands) are widespread. They are used to identify aeolian transport pathways. The mU/fS-ratio (5-11 µm/48-70 µm) among primary loess opposes the two grain size fractions being most sensitive to varying accumulation conditions. The first fraction is attributed to long-distance transport in high suspension clouds whereas the latter represents local transport in saltation mode. The ratio shows strong correlation with elevation ( R2 = 0.77). Thus, it indicates a relatively higher far-traveled dust supply in mountainous areas (>3000 m above sea level [a.s.l.]) compared to the foreland. The contribution of westerlies to high mountain loess deposits is considered likely. Hereby, the influence of the geomorphological setting on grain size composition of aeolian sediments becomes apparent: the contribution from distant dust sources is ubiquitous in the study area. However, the far-distance contribution may be reduced by the availability of fine sand provided in low topography settings. Plain foreland areas support fine sand deflation from supplying river beds, allowing the formation of sandy loess in foreland areas and intramontane basins. In contrast, high mountain topography inhibits strong sand deflation into loess deposits. Eastern parts of the Hexi Corridor show higher aeolian sand occurrence. In contrast, the western parts are dominated by gravel gobi surfaces. This is attributed to higher sand supply in eastern parts provided by the Badain Jaran Desert and fluvial storages as sand sources. Copyright © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

In this study, wind tunnel tests were performed to determine the relationships between sediment transport, the surface moisture content, and wind velocity using beach sands from a tropical humid coastal area of China. The variation in the properties of the creep proportion, relative decay rate as a function of height, and average saltation height in the flux profile were determined. Sand transport was measured using a standard vertical sand trap. The creep proportion (i.e., the proportion of the particles that move along the surface rather than undergoing saltation) and relative decay rate decreased and more particles were ejected to higher positions as moisture content and wind velocity increased. The creep proportion ranged between 0.12 and 0.33, and averaged 0.22. The creep proportion and relative decay rate decreased abruptly at moisture contents between 0.587 and 1.448%; the latter value was close to 1.591%, the moisture content at a matric potential of −1.5 MPa. This moisture content limit may indicate a change in the form of soil water from adsorbed films on particle surfaces to capillary forces created by inter-particle water bridges. The surface moisture content therefore appears to decisively determine the degree of the restraint on particle entrainment by the wind. The average heights, below which 25, 50, 75, and 90% of sand transport occurred, increased with increasing moisture content (except at 0.231% moisture content) and wind velocity. The mean saltation height at various wind velocities increased linearly with increasing moisture content. [ABSTRACT FROM AUTHOR]

The wind fetch effect is important to wind erosion and aeolian transport and controls aeolian flux. It is useful to study the wind fetch effect in determining the aeolian transport mechanism and improving our knowledge of aeolian physics and wind erosion. In this paper, multichannel samplers measure aeolian transport at different heights above an artificial Gobi surface in the southeastern region of the Tengger Desert. The results show that aeolian transport flux can be expressed as an exponential function of height. Wind fetch obviously affects aeolian flux and aeolian transport. The coefficients and relative decay rate of aeolian flux decrease and then increase with increasing wind fetch distance. Aeolian transport depends on the height and fetch distance; aeolian transport increases and then decreases with increasing fetch distance, reaching a maximum at a fetch distance of about 34 m at the very near surface. The fetch distance of maximum aeolian transport tends to increase with height. [ABSTRACT FROM AUTHOR]

This article reported a wind tunnel test of sediment transport related to surface moisture content and wind velocity using sands from tropical humid coastal area. A 1 mm-thick portion of surface sand was scraped using a self-made sediment sampler, and the gravimetric moisture content was determined. Sand transport was measured via a standard vertical sand trap with a 60 cm height. The result shows that the sand transport profile above the wet surface can be expressed with an exponential equation. In general, the influence of moisture content on sand transport profile mainly focuses on the bottom of the blowing sand cloud. Meanwhile, with moisture content increased, total sand transport dropped, and a relatively larger proportion is transported at greater heights. The vertical movement of particles on higher moisture surface (0.587% < M < 1.448%) is more sensitive to moisture content variation as compared to those on low wet surface ( M < 0.587%), total sand transport rate tends to be rather low (0.99 g cm s) when M > 1.448%. The total sand transport rate varying with moisture content is divided into three regions of differing gradient at the moisture contents of 0.587 and 1.448%. The gradient of the curve reflected the different influences of the various water forms in surface sediments. The higher moisture surface ( M > 1.448%) merely functions as a transport plain for the saltation material. Surface moisture content was the dominant control factor for saltation activity between the moisture contents of 0.587 and 1.448%, wind velocity could resume control saltation after the surface dried to the extent ( M < 0.587%). [ABSTRACT FROM AUTHOR]

Zibars are aeolian bedforms created by armoring of the surface by coarse grains. The existence and movement of these grains strongly influence zibar morphodynamics. Although aeolian sediment transport has been investigated for arid surface processes with a range of grain sizes, the measurement durations were short, making it difficult to establish the relationship between microscopic aeolian transport processes and macroscopic geomorphological processes. In the present study, we conducted field observations of aeolian sediment transport above a zibar in northern China's Kumtagh Sand Sea with a segmented sand trap. During six measurement periods throughout 2014, the sampler collected 314.76 kg of sediments within 1 m above the ground. The directional variation indicated that about 52.5% of the sediments came from the north, northeast, and northwest; the southeast provided the least sediments. The strongest aeolian transport occurred between August and October; the weakest was in winter. The aeolian sediment flux decreased with height, and 54% of particles were transported within 0.1 m above the ground. The transport profiles fit an exponential decay function. The flux's directional variation resulted from the combined effects of sediment availability and wind regime, so the calculated net transport differed from the drift potential. The seasonal and directional variations of aeolian transport significantly affect the morphodynamic process of zibars. The trend and the internal sedimentary structure of zibars were closely related to the aeolian transport process. • Aeolian transport over a zibar surface were measured with a new sand trap • The strongest aeolian transport occurred in autumn and blown from the north • The combination of sediment availability and wind regime affects aeolian transport [ABSTRACT FROM AUTHOR]