A New Formula for Estimating the Threshold Wind Speed for Snow Movement

He, Siwei; Ohara, N.

doi:10.1002/2017ms000982

Cited by 29 publications

(33 citation statements)

References 50 publications

(116 reference statements)

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“…Nearly all existing models of the initiation of aeolian rolling and saltation transport (including sand transport (Bagnold, ; Burr et al, ; Claudin & Andreotti, ; Cornelis & Gabriels, ; de Vet et al, ; Durán et al, ; Duan, Cheng, & Xie, ; Edwards & Namikas, ; Iversen et al, , ; Iversen & White, ; Kok & Renno, ; Lu et al, ; Merrison et al, ; Shao & Lu, ), drifting snow (He and Ohara, ; Lehning et al, ; Schmidt, ), and the transport of regolith dust by outgassed ice on the comet 67P/Churyumov‐Gerasimenko (Jia et al, )) predict

τ_{t}^{In}

from the balance between aerodynamic forces and/or torques and resisting forces and/or torques acting on a bed particle. Even though many of these models do not consider peaks of the aerodynamic force, and some of them do not treat

τ_{t}^{In}

as what it is (i.e., the threshold at which the fluid entrainment probability exceeds zero, see above), they are conceptually very similar and mainly differ in the empirical equations that they use for the aerodynamic and cohesive interparticle forces.…”

Section: Fluid Entrainment By Turbulent Flowsmentioning

confidence: 99%

The Physics of Sediment Transport Initiation, Cessation, and Entrainment Across Aeolian and Fluvial Environments

Pähtz

Clark

Valyrakis

et al. 2020

Reviews of Geophysics

121

149

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Predicting the morphodynamics of sedimentary landscapes due to fluvial and aeolian flows requires answering the following questions: Is the flow strong enough to initiate sediment transport, is the flow strong enough to sustain sediment transport once initiated, and how much sediment is transported by the flow in the saturated state (i.e., what is the transport capacity)? In the geomorphological and related literature, the widespread consensus has been that the initiation, cessation, and capacity of fluvial transport, and the initiation of aeolian transport, are controlled by fluid entrainment of bed sediment caused by flow forces overcoming local resisting forces, whereas aeolian transport cessation and capacity are controlled by impact entrainment caused by the impacts of transported particles with the bed. Here the physics of sediment transport initiation, cessation, and capacity is reviewed with emphasis on recent consensus‐challenging developments in sediment transport experiments, two‐phase flow modeling, and the incorporation of granular physics' concepts. Highlighted are the similarities between dense granular flows and sediment transport, such as a superslow granular motion known as creeping (which occurs for arbitrarily weak driving flows) and system‐spanning force networks that resist bed sediment entrainment; the roles of the magnitude and duration of turbulent fluctuation events in fluid entrainment; the traditionally overlooked role of particle‐bed impacts in triggering entrainment events in fluvial transport; and the common physical underpinning of transport thresholds across aeolian and fluvial environments. This sheds a new light on the well‐known Shields diagram, where measurements of fluid entrainment thresholds could actually correspond to entrainment‐independent cessation thresholds.

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τ_{t}^{In}

τ_{t}^{In}

Section: Fluid Entrainment By Turbulent Flowsmentioning

confidence: 99%

The Physics of Sediment Transport Initiation, Cessation, and Entrainment Across Aeolian and Fluvial Environments

Pähtz

Clark

Valyrakis

et al. 2020

Reviews of Geophysics

121

149

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“…Mean flow entrainment models derive a transport initiation threshold Shields number from a force balance, and/or torque balance, between mean fluid forces and resisting contact forces acting on a representative particle resting on the bed surface (Agudo et al, 2017;Ali & Dey, 2016;Bagnold, 1936Bagnold, , 1941Bravo et al, 2014Bravo et al, , 2017Claudin & Andreotti, 2006;Dey, 1999Dey, , 2003Dey & Papanicolaou, 2008;Duan et al, 2013;Durán et al, 2011;Edwards & Namikas, 2015;He & Ohara, 2017;Iversen et al, 1976Iversen et al, , 1987Iversen & White, 1982;Lee et al, 2012;Lehning et al, 2000;Ling, 1995;Lu et al, 2005;Luckner & Zanke, 2007;Recking, 2009;Rousar et al, 2016;Schmidt, 1980;Shao & Lu, 2000;Vollmer & Kleinhans, 2007;Ward, 1969;Wiberg & Smith, 1987;White, 1940;Wu & Chou, 2003). Many of these models have been proposed to reproduce the Shields diagram, which displays two kinds of fluvial thresholds: a threshold obtained from extrapolating measurements of the transport rate to (nearly) vanishing transport and visual measurements of the initiation threshold of individual transport (see section 4.3 for details).…”

Section: Comparison With Previous Threshold Models 441 Mean Flow Ementioning

confidence: 99%

The Cessation Threshold of Nonsuspended Sediment Transport Across Aeolian and Fluvial Environments

2018

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Using particle‐scale simulations of nonsuspended sediment transport for a large range of Newtonian fluids driving transport, including air and water, we determine the bulk transport cessation threshold normalΘtr by extrapolating the transport load as a function of the dimensionless fluid shear stress (Shields number) Θ to the vanishing transport limit. In this limit, the simulated steady states of continuous transport can be described by simple analytical model equations relating the average transport layer properties to the law of the wall flow velocity profile. We use this model to calculate normalΘtr for arbitrary environments and derive a general Shields‐like threshold diagram in which a Stokes‐like number replaces the particle Reynolds number. Despite the simplicity of our hydrodynamic description, the predicted cessation threshold, both from the simulations and analytical model, quantitatively agrees with measurements for transport in air and viscous and turbulent liquids despite not being fitted to these measurements. We interpret the analytical model as a description of a continuous rebound motion of transported particles and thus normalΘtr as the minimal fluid shear stress needed to compensate the average energy loss of transported particles during an average rebound at the bed surface. This interpretation, supported by simulations near normalΘtr, implies that entrainment mechanisms are needed to sustain transport above normalΘtr. While entrainment by turbulent events sustains intermittent transport, entrainment by particle‐bed impacts sustains continuous transport. Combining our interpretations with the critical energy criterion for incipient motion by Valyrakis and coworkers, we put forward a new conceptual picture of sediment transport intermittency.

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“…Indeed, the dynamics and the initiation of the transport in saltation, and ultimately in turbulent suspension, depend on the properties of the snow surface (type of crystals, cohesion, and roughness). Schmidt (1980), Lehning et al (2000) and He and Ohara (2017) have proposed formulations for the threshold wind speed of snow transport accounting for cohesion due to sintering between snow grains at the surface. The lowest threshold wind speeds are found for fresh-fallen dendritic snow characterized by low cohesion (Guyomarc'h and Merindol, 1998).…”

Section: Post-depositional Processes Drifting and Blowing Snowmentioning

confidence: 99%

The Seasonal Snow Cover Dynamics: Review on Wind-Driven Coupling Processes

2018

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The temporal evolution of seasonal snow cover and its spatial variability in environments such as mountains, prairies or polar regions is strongly influenced by the interactions between the atmospheric boundary layer and the snow cover. Wind-driven coupling processes affect both mass and energy fluxes at the snow surface with consequences on snow hydrology, avalanche hazard, and ecosystem development. This paper proposes a review on these processes and combines the more recent findings obtained from observations and modeling. The spatial variability of snow accumulation across multiple scales can be associated to wind-driven processes ranging from orographic precipitation at large scale to preferential-deposition of snowfall and wind-induced transport of snow on the ground at smaller scales. An overview of models of varying complexity developed to simulate these processes is proposed in this paper. Snow ablation is also affected by wind-driven processes. Over continuous snow covers, turbulent fluxes of latent and sensible heat, as well as blowing snow sublimation, modify the mass, and energy balance of the snowpack and their representation in numerical models is associated with many uncertainties. As soon as the snow cover becomes patchy in spring local heat advection induces the development of stable internal boundary layers changing heat exchange toward the snow. Overall, wind-driven processes play a key role in all the different stages of the evolution of seasonal snow. Improvements in process understanding particularly at the mountain-ridge and the slope scale, and processes representations in models at scales up to the mountain range scale, will be the basis for improved short-term forecast and climate projections in snow-covered regions.

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A New Formula for Estimating the Threshold Wind Speed for Snow Movement

Cited by 29 publications

References 50 publications

The Physics of Sediment Transport Initiation, Cessation, and Entrainment Across Aeolian and Fluvial Environments

The Physics of Sediment Transport Initiation, Cessation, and Entrainment Across Aeolian and Fluvial Environments

The Cessation Threshold of Nonsuspended Sediment Transport Across Aeolian and Fluvial Environments

The Seasonal Snow Cover Dynamics: Review on Wind-Driven Coupling Processes

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