Back analysis of drifting-snow measurements over an instrumented mountainous site

Abstract

ABSTRACT. The NEMO numerical model of drifting snow, whose general outlines are presented in this paper, is based on a physical model for saltation and turbulent diffusion. The model needs a set of input parameters including fall velocity, threshold shear velocity, shear velocity, mass concentration and roughness, which are obtained from empirical formulae and wind speed measured at a given height. To better determine the required field data in an alpine context, our experimental site, Col du Lac Blanc (2700 m a.s.l.), French Alps, was first equipped with one anemometer and blowing-snow acoustic sensors, which proved not to be accurate enough for research purposes in the current state of development even though a new calibration curve was used. We therefore set up a Snow Particle Counter and we returned to the traditional, robust mechanical traps and a 10 m mast with six anemometers, two temperature sensors and a depth sensor to better determine friction velocity and aerodynamic roughness. Based on the studied drifting-snow events we conclude: (1) the proportionality of the aerodynamic roughness to the square of the friction velocity was confirmed, but with a varying proportionality ratio depending on the snowdrift event; (2) values of s U F were relatively well approximated by empirical formulae from data originating from Antarctica, and (3) snowdrift concentration profiles obtained by Pomeroy's semi-empirical formulae for the saltation layer coupled with a theoretical approach for the diffusion layer overestimated the concentration profiles for the studied blowing-snow event.

Transport of Snow by the Wind: A Comparison Between Observations in Adélie Land, Antarctica, and Simulations Made with the Regional Climate Model MAR

“…This is why we use our RCM here with a high horizontal and vertical resolution. Nevertheless the issues raised concerning the accuracy of the Ingénierie Acoustique & Vibratoire (IAV) FlowCapt acoustic sensors (Chritin et al 1999) used in the present study have, up to now, prevented a reliable quantitative comparison of the blowing snow flux (Cierco et al 2007;Naaim-Bouvet et al 2010). …”

“…The calibration of FlowCapt results in overestimation of the blowing snow flux that is all the larger due to the high wind speed (Cierco et al 2007;Naaim-Bouvet et al 2010). As the winds responsible for the transport of blowing snow are very strong in Antarctica, considerable overestimation of the blowing snow flux can be expected.…”

Transport de neige par le vent sur un site de haute montagne :de la modélisation à l’observation, de l’observation à la modélisation

“…Les processus physiques en jeu ont pu être étu-diés plus finement pour pouvoir être à terme mieux pris en compte dans les modèles [Naaim-Bouvet F., 2008]. Cette vision reste bien sur schématique car dans le même temps, l'instrumentation permettait également une estimation des Un des paramètres clef, dont la mesure est encore soumise à controverse, est le flux de neige transporté.…”

“…Les premiers résultats obtenus grâce à ce renforcement d'instrumentation ont montrés que [Naaim-Bouvet F., 2008], , : -La proportionnalité de la rugosité aérodynamique avec la vitesse de frottement semble confirmée (figure 9) avec un coefficient de proportionnalité dépendant de l'évènement. Cependant la faible valeur du coefficient de corrélation et la grande variabilité des résultats reste source d'interrogation.…”

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

“…In this study, the observed threshold wind speed was estimated from several relatively long-term snow flux observation data collected by the FlowCapt acoustic sensors, which was designed for continuous and automatic recording of snow flux in the air (Chritin et al, 1999). A number of studies have demonstrated that the FlowCapt sensor is capable of detecting drifting snow or blowing snow (Naaim-Bouvet et al, 2010;Bellot et al, 2011;Das et al, 2012;Trouvilliez et al, 2015). Wind speed required for snow flux to occur and the corresponding snow deposition time and temperature were extracted.…”