Threshold Wind-Speeds and Elastic Impact in Snow Transport

Abstract

Cohesive forces are added to the analysis offorces on sand and soil particles to show that fluid drag, alone, often cannot initiate movement of a snow surface. The impact force of saltating ice spheres, however, can easily provide the force to break cohesive bonds, according to these calculations. The argument suggests a balance between the distribution of bond strengths of exposed surface particles and the distribution of saltation trajectory h eights. RESUME. Seuil des vitesse de vent et [,impact ilastique pOllr le transport de la Ileige. Les forces de cohesion s'ajoutent a l'analyse des forces s'exen;:ant sur les particules de sable ou de sol pour montrer que l'entrinement par le fluide, seul, est souvent insuffisant pour provoquer la mise en mouvement d'une surface de neige. Cependant, la force d'impact d'une sph ere de glace en saltation peut aisement briser les liens de la cohesion, selon ces calculs. La conclusion suggere un bilan entre la distribution des resistances des liens entre les particules des surfaces exposees et la distribution des hauteurs de trajectoire de la saltation. ZUSAMMENFASSUNG. Schwellenwerte der Windgeschwindigkeit ulld elastischer Aufprall beim Schneetrallsport. Als Beweis dafur, dass fliessende Verschleppung alIein oft keine Bewegung einer Schneedecke einleiten kann, werden kohasive Krafte in die Analyse der Kraftwirkung auf Sand-und Bodenpartikel eingefuhrt. Die AufpralIkraft springender Schneekugeln genugt jedoch zur Uberwindung kohasiver Bindungen, wie aus diesen Berechnungen hervo rgeht. Infolgedessen lasst sich ein Gleichgewicht zwischen der Verteilung der Bindungskrafte in exponierten Oberflachenteilch en und jener def Hohen der Sprungbahnen annehmen.

Transport rate of drifting snow and the mean wind speed profile

“…By adding cohesion to Chepil's (1959) analysis of forces on an exposed soil grain, Schmidt (1980) concluded that time and temperature histories of the snow surface were much more important than particle weight in determining the wind speed required for incipient drifting. Approaches that relate threshold shear stress to particle size are not directly applicable in the case of windblown snow.…”

Cohesion‐Induced Enhancement of Aeolian Saltation

“…Our ability to quantify and predict these processes is still impaired by a limited understanding of the fundamental controls on sand and snow transport, in particular, as affected by the cohesion of the granular bed. Snow and wet sand grains, in fact, develop strong cohesive forces in form of sintered ice bonds (Schmidt, 1980) and water menisci (Ravi et al, 2004).…”

High‐Precision Measurement of 187Os/188Os Isotope Ratios of Nanogram to Picogram Amounts of Os in Geological Samples by N‐TIMS using Faraday Cups Equipped with 1013 Ω Amplifiers

“…In addition, the 187 Os/ 188 Os ratios also differ from the results obtained from secondary EM measurements using a Triton TIMS at the GIG, CAS laboratory over the past 6 years, ranging from 0.17198 ± 19 to 0.1858 ± 47 (2SE, n = 50 for each aliquot and each analysis) with a mean value of 0.181 ± 12 (2s, n = 6). The published 187 Os/ 188 Os ratios for this reference material also have a large variation and are 0.176 ± 28 (2SE), as measured by static FCs with conventional 10 11 Ω amplifiers (Chu et al 2015b), and from 0.15824 ± 19 (2SE) to 0.15815 ± 17 (2SE) as measured by secondary EM (Schmidt and Snow 2002). It is obvious that the 187 Os/ 188 Os ratios of WGB-1 are variable between different sample aliquots and different laboratories.…”