Measurement of snow particle size and velocity in avalanche powder clouds

• Published in: Journal of Glaciology
• Main Authors: Ito, Yoichi, Naaim-Bouvet, Florence, Nishimura, Kouichi, Bellot, Hervé, Thibert, Emmanuel, Ravanat, Xavier, FONTAINE, Firmin
• Other Authors: Erosion torrentielle neige et avalanches (UR ETGR (ETNA)), Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA), Graduate School of Environmental Studies Nagoya, Nagoya University, Snow and Ice Research Center, NIED
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2017
• Subjects: powder snow cloud; particle speed; particle size; avalanche; [SDE]Environmental Sciences; [SDU]Sciences of the Universe [physics]; Journal of Glaciology
• Online Access: https://hal.archives-ouvertes.fr/hal-01985000; https://doi.org/10.1017/jog.2016.130

International audience Particle size, particle speed and airflow speed have been measured in the powder snow clouds of avalanches to investigate the suspension and transportation processes of snow particles. The avalanches were artificially triggered at the Lautaret full-scale avalanche test-site (French Alps) where an ultrasonic anemometer and a snow particle counter were setup in an avalanche track for measurements. Relatively large particles were observed during passage of the avalanche head and then the size of the particles slightly decreased as the core of the avalanche passed the measurement station.The particle size distribution was well fitted by a gamma distribution function. A condition for suspension of particles within the cloud based on the ratio of vertical velocity fluctuation to particle settling velocity suggests that the large particles near the avalanche head are not lifted up by turbulent diffusion, but rather ejected by a process involving collisions between the avalanche flow and the rough snow surface. Particle speeds were lower than the airflow speed when large particles were present in the powder cloud.