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

Abstract

Threshold wind speed for snow movement is one of the most important parameters describing the wind‐transport snow process. A majority of previous studies used empirical and constant threshold wind speeds while the variations of atmosphere condition and snow age seem to greatly affect the snow settlement process. This study tested the hypothesis that the threshold wind speed for snow transport increases as deposition time passed since last snowfall by introducing a new formula of the threshold wind speed for snow movement. It was theoretically derived based on the sintering process modeling and the moment balance of a snow particle. Through this formula, the influences of snow particle size, temperature, and deposition time on the threshold wind speed were explicitly taken into consideration. However, two empirical parameters in the sintering process modeling remained in the new formula, and they were determined by a calibration‐validation procedure using the field observed snow flux data. The snow flux and meteorological data collected at the ISAW stations (http://www.iav.ch) including large number of snow transport events during five winter seasons were used to test this formula. It was shown that the new formula qualitatively described the threshold wind speed required for the incipient motion of snow under various conditions in the natural environment of the Alps.

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

“…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 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 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.…”

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

“…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).…”

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

“…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).…”