Fragmentation of wind‐blown snow crystals

• Published in: Geophysical research letters 2017-05, Vol.44 (9), p.4195-4203
• Main Authors: Comola, Francesco, Kok, Jasper F., Gaume, Johan, Paterna, Enrico, Lehning, Michael
• Format: Article
• Language: English
• Subjects: aeolian transport; Albedo; Albedo (solar); Alpine regions; Avalanches; Blowing; Blowing snow; Climate; Climate change; Climate models; Computer simulation; Crystallization; Crystals; Dendritic structure; Energy; fractal; Fragmentation; Fragments; Geophysics; Hazards; Mass; Mathematical models; Mountain regions; Numerical simulations; Particle distribution; Particle size; Particle size distribution; saltation; Scale models; Scaling; Self-similarity; Size distribution; Snow; Snow avalanches; Snow cover; Snow crystals; Snowfall; snowflake; Snowflakes; Statistical mechanics; Theory; turbulence; Water resources; Water resources management; Wind tunnels; Winds
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1002/2017GL073039

Understanding the dynamics driving the transformation of snowfall crystals into blowing snow particles is critical to correctly account for the energy and mass balances in polar and alpine regions. Here we propose a fragmentation theory of fractal snow crystals that explicitly links the size distribution of blowing snow particles to that of falling snow crystals. We use discrete element modeling of the fragmentation process to support the assumptions made in our theory. By combining this fragmentation model with a statistical mechanics model of blowing snow, we are able to reproduce the characteristic features of blowing snow size distributions measured in the field and in a wind tunnel. In particular, both model and measurements show the emergence of a self‐similar scaling for large particle sizes and a systematic deviation from this scaling for small particle sizes. Plain Language Summary During snowfall, wind‐blown snowflakes shatter upon impact with the surface and produce small ice fragments. The size of these fragments affects important properties of the snow cover, such as its albedo, predisposition to melting, and likelihood of avalanche release. Snowflake fragmentation has thus significant implications for water resources management, climate change, and human safety. Despite such relevance, very little is known about how snow fragmentation occurs. Here we propose a new theory, based on the fascinating dendritic structure of some snowflakes, to describe these fragmentation processes. We show that the results of our theoretical model are in good agreement with numerical simulations and experimental measurements. This is the first time that an effective fragmentation theory is proposed to explain the transition from snowfall crystals to blowing snow particles. If accounted for in larger‐scale models, our results may thus contribute to improve quantifications of climate change effects in Antarctica, water resources management, and avalanche danger in mountain regions. Key Points The fragmentation dynamics of dendritic snowflakes can be predicted based on their fractal structure Snow fragmentation can explain the transition from the size distribution of snowfall crystals to that of blowing snow particles The typical features of blowing snow size distributions emerge from the fractal shape of snowflakes and from turbulence suspension