Dynamics of Wind Erosion

Chepil, W. S.

doi:10.1097/00010694-194511000-00005

Cited by 183 publications

(59 citation statements)

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“…Based on equation (9), we calculate u *, it /u *, ft = 0.813 ± 0.018, 0.863 ± 0.027, and 0.837 ± 0.007 at Jericoacoara, Rancho Guadalupe, and Oceano, respectively (Table 1). These values are consistent with laboratory measurements (Bagnold, 1937;Chepil, 1945;Iversen & Rasmussen, 1994) and numerical predictions (Kok, 2010a) of u *, it /u *, ft ≈ 0.82 (i.e., τ it /τ ft ≈ 0.67). As with threshold stresses, we compute uncertainties in u *, it /u *, ft by following standard error propagation methods (Appendix B).…”

Section: Threshold Ratiossupporting

confidence: 89%

“…Calculated threshold values and their uncertainties, illustrated in Figure 4a and listed in Table 1, are comparable to wind tunnel measured values of τ ft (Bagnold, 1937;Chepil, 1945;Fletcher, 1976;Kok et al, 2012, Figure 5;Zingg, 1953) and τ it (Bagnold, 1937;Chepil, 1945;Iversen & Rasmussen, 1994;B. Li & McKenna Neuman, 2012;Kok et al, 2012, Figure 21) for sediment bed grain sizes similar to those measured at our field sites.…”

Section: Fluid and Impact Thresholdssupporting

confidence: 87%

“…The ratio of impact and fluid thresholds governing this hysteresis depends primarily on the particle-fluid density ratio, which determines the relative contributions of particle impacts and direct fluid lifting to particle entrainment (Kok, 2010b;Pähtz & Durán, 2017). On Earth, the experimentally (Bagnold, 1937;Chepil, 1945;Iversen & Rasmussen, 1994) and numerically (Kok, 2010b) predicted ratio of impact and fluid threshold shear velocities u *it /u *ft is approximately 0.82, whereas u *it /u *ft is predicted to be as low as 0.1 on Mars (Kok, 2010a).…”

Section: Introductionmentioning

confidence: 99%

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Distinct Thresholds for the Initiation and Cessation of Aeolian Saltation From Field Measurements

2018

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Wind‐blown sand and dust models depend sensitively on the threshold wind stress. However, laboratory and numerical experiments suggest the coexistence of distinct fluid and impact thresholds for the initiation and cessation of aeolian saltation, respectively. Because aeolian transport models typically use only a single threshold, existence of separate higher fluid and lower impact thresholds complicates the prediction of wind‐driven transport. Here we extend the statistical Time Frequency Equivalence Method to derive the first field‐based estimates of distinct fluid and impact thresholds from high‐frequency wind and saltation measurements at three field sites. Our measurements show that when saltation is mostly inactive, its instantaneous occurrence is governed primarily by wind exceedance of the fluid threshold. As saltation activity increases, so too does the relative importance of the impact threshold, until it dominates under near‐continuous transport conditions. Although both thresholds are thus important for high‐frequency saltation prediction, our results suggest that the time‐averaged saltation flux is primarily governed by the impact threshold.

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Section: Threshold Ratiossupporting

confidence: 89%

Section: Fluid and Impact Thresholdssupporting

confidence: 87%

Section: Introductionmentioning

confidence: 99%

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Distinct Thresholds for the Initiation and Cessation of Aeolian Saltation From Field Measurements

2018

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“…For a loose sand grain of given size (Dp) to be launched from the bed, the aerodynamic force exerted by airflow and the forces due to the impacts of other moving particles must overcome the effect of weight, friction angle and inter-particle cohesion that tend to resist entrainment (Rumpel, 1985;Anderson, 1986;Gillette and Stockton 1986;Mitha et al, 1986;Willetts and Rice, 1986;Anderson and Haff, 1988;Werner and Haff, 1988;Willetts et al, 1991;McEwan et al, 1992;Li and Martz, 1995;Shao, 2000). The threshold wind friction velocity (u* t ) is therefore a parameter of crucial importance in the quantification of the intensity of sand movement (Bagnold, 1941;Chepil, 1945;Kawamura, 1951;Zingg, 1953;Owen, 1964;Lettau and Lettau, 1977;White, 1979;Shao and Li, 1999). Once entrained, the coarser sand grains move close to the ground in the socalled 'saltation layer' whose height is typically 1 m. Conversely, grains of smaller size can be uplifted by turbulence and transported higher and farther from their original source.…”

Section: Rationalementioning

confidence: 99%

Aeolian erosion and sand transport over the Mejillones Pampa in the coastal Atacama Desert of northern Chile

et al. 2010

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“…[2] Aeolian sand transport is an important process in many research fields of physics, geosciences, agriculture, and engineering. As saltation is the primary mode of wind-blown transport on beach intertidal and supratidal zones, much effort has been made to understand saltation systems including the aerodynamic entrainment of sand, acceleration of sand grains through the air stream, and transport of sand in steady winds [Bagnold, 1941;Chepil, 1945;Kawamura, 1951;Owen, 1964;White, 1979;Iversen and White, 1982;Ungar and Haff, 1987;Werner, 1990;Anderson and Haff, 1991;Shao and Raupach, 1992;Iversen and Rasmussen, 1999;Shao and Lu, 2000;Roney and White, 2004;Sorensen, 2004].…”

Section: Introductionmentioning

confidence: 99%

Observations of wind‐blown sand under various meteorological conditions at a beach

Udo¹,

Kuriyama²,

Jackson³

2008

J. Geophys. Res.

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[1] Field observations were conducted on a natural, open ocean beach system in Japan to investigate characteristics of wind-blown sand transport under various weather conditions including a storm event. Data sets over periods of several hours included blown sand impact counts, three-dimensional wind conditions, hourly precipitation, and moisture content of the sediment surface. The intermittent blown sand impact data shifted by 1 s ahead of the wind velocity correlated with the wind velocity during a no-rainfall period (for an assumed dry surface) and in the longshore wind direction (for sufficiently long fetch length). The 5-min mean wind velocity/impact counts relationship was well constrained by both second-and third-order polynomial fitting of velocity under similar weather conditions. During a no-rainfall period and in the longshore wind direction, the relationship between the wind velocity and sand flux estimated from the counts coincides with existing studies in wind tunnel experiments. The sand flux, however, decreased by 1 order of magnitude because of a change in the wind direction from longshore to cross-shore and then by more than 1 order of magnitude because of an increase in the moisture content. Threshold wind velocity calculated using the time fraction equivalence method with the impact counts and the horizontal wind velocity in 5-min sampling periods was approximately equal to the value predicted using Bagnold's equation during the no-rainfall period and increased significantly during the rainfall phase. The sand flux sensor has several limitations for complex conditions in the field; however, it provides a number of characteristics of sand transport under various meteorological conditions.

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Dynamics of Wind Erosion

Cited by 183 publications

References 0 publications

Distinct Thresholds for the Initiation and Cessation of Aeolian Saltation From Field Measurements

Distinct Thresholds for the Initiation and Cessation of Aeolian Saltation From Field Measurements

Aeolian erosion and sand transport over the Mejillones Pampa in the coastal Atacama Desert of northern Chile

Observations of wind‐blown sand under various meteorological conditions at a beach

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