A numerical simulation of the effects of snow particle shapes on blowing snow development

Abstract

[1] Snow particle shape is an important factor affecting the development of blowing snow. In this paper, we established a numerical model of blowing snow development and compared the changes in numbers of endurance spherical, ellipsoidal, star, hexagonal prism, and cylindrical snow particles in the air with time and their transport rates with time and height during the development. The following are the major conclusions.(1) The effects of snow particle shapes on the numbers of endurance snow particles in the air and the transport rates of snow vary so dramatically, even in a few orders of magnitude, that snow particles should not be simplified as spheres or ellipsoids in simulation. (2) In the logarithmic wind field, the potential energy of spherical snow particles obtained from wind at higher heights is much greater than that of star snow particles at lower heights. Thus, the snow particles with greater energy can eject more snow particles when precipitating to the snow bed. (3) The five snow particles differ in their duration to reach dynamic equilibrium but not in the variation of the numbers of endurance snow particles in the air and the snow transport rates with time. (4) At dynamic equilibrium, the number of endurance snow particles in spherical, ellipsoidal, and star shapes and their heights and transport rates with time are at least one order of magnitude larger than those of the endurance snow particles in hexagonal prism and cylindrical shapes.

Numerical simulation of drifting snow sublimation in the saltation layer

“…In wind-blown snow, snow particles are entrained and transported by the wind, while the wind field is simultaneously influenced by the snow particles, indicating a self-regulating feedback mechanism between the saltating particles and the wind field. In this mechanism, the drag force associated with particle acceleration reduces the wind velocity in the saltation layer, thus limiting the entrainment of further particles 21 . At a given wind speed, the number of snow particles in the saltation layer initially increases rapidly with time and then decreases gradually until it reaches a steady state, i.e., the number of particles in the layer will not increase further.…”

“…At a given wind speed, the number of snow particles in the saltation layer initially increases rapidly with time and then decreases gradually until it reaches a steady state, i.e., the number of particles in the layer will not increase further. The time for the wind-blown snow to reach steady state decreases as the friction velocity increases 21 22 . Figure 1 shows the temporal evolution of DSS with different friction velocity (ranging from 0.25 m/s to 0.5 m/s) under different environmental conditions, with a temperature of 263.15 K or 268.15 K and humidity of 0.3 or 0.8.…”

“…The simulation of DSS includes simulating the snow saltation process and numerically calculating the sublimation of saltating particles. Snow particle saltation can be divided into four sub-processes including the aerodynamic entrainment, particle trajectories, particle-bed collisions, and wind modification 21 .…”

“…Basic equations for snow particle trajectory. Assuming that the drifting snow grain is spherical and subject to gravity, buoyancy force and drag force in the air, its motion equations are 21 where m p and W g are the mass and weight of the snow particle, respectively; U f , V f , U p , and V p are the horizontal and vertical velocities of the airflow and the snow particle, respectively; is the relative velocity between the airflow and the snow particle; x p and y p are the horizontal position and vertical height of the snow particle, respectively; and are the buoyancy force and the drag force applied on the snow particle, respectively; ρ f is the air density; D is the diameter of snow particle; g is the acceleration of gravity; and C D is the drag coefficient.…”

The impacts of moisture transport on drifting snow sublimation in the saltation layer

“…where RH is the relative humidity of air, K is the molecular thermal conductivity of the atmosphere (0.024 J m −1 s −1 K −1 ), D v is the molecular diffusivity of water vapor in the atmosphere, R v is the gas constant for water vapor (461.5 J kg −1 K −1 ), e s is saturated vapor pressure with respect to an ice surface, and Nu and Sh are the Nusselt number and the Sherwood number, respectively, both of which are dimensionless and depend on the wind velocity and particle size (Thorpe and Mason, 1966;Lee, 1975).…”