Structure of drifting snow simulated by Lagrangian particle dispersion model coupled with large-eddy simulation using the lattice Boltzmann method
Tsutomu Watanabe, Shuhei Ishikawa, Masayuki Kawashima, Kou Shimoyama, Naoyuki Onodera, Yuta Hasegawa, Atsushi Inagaki
Abstract
This paper describes simulations of drifting snow in the atmospheric surface layer. We develop a Lagrangian particle dispersion model coupled with a large-eddy simulation code based on the central-moment lattice Boltzmann method. The model reproduces typical features of drifting snow observed in the field, such as the dependency of the mass transport rate on the flow velocity, the kink in the vertical mass flux profile near the saltation layer height, and the variations in particle size distribution with the flow velocity and height. The saltation layer height determined directly from the net forces acting on the airborne particles is found to increase monotonically with increasing flow velocity, unlike conventional estimates, which tend to saturate as the flow velocity increases. Using the vertical transition probabilities of individual particles, the transition from saltation to suspension is confirmed to occur near the estimated saltation layer height. A composite analysis shows that snow streamers (dense particle clouds elongated in the streamwise direction and meandering laterally in the saltation layers) are closely associated with small-scale low-speed streaks in the near-surface flows. Particularly dense snow streamers are more likely to occur around streaks modulated by high-speed coherent flows of much larger spatial scales.