A General Model Of Blowing Snow: Saltation And Suspension

The polar ice sheets,mountain glaciers,snowy area in high latitude of Northern Hemisphere,whose main source is snow,have profound influence on the global hydrologic cycle,climate change and ecological system.Extensive researches showed that blowing snow was an important method to change the snow distribution.Saltation and suspension are the main movement ways of snow grains in the blowing snow.In the current blowing snow model,due to hypothesis that the snow particles have good followability to the wind field,the two-fluid model cannot accurately describe the movement of saltating particle;due to the large amount of calculations,the Euler-Langentlang model has difficulty in describing the suspended snow particles.Therefore,neither of them can accurately describe the salatation and suspension of the snow particles at the same time.In addition,there is currently a lack of accurate and effective determination conditions of saltation and suspension for blowing snow.The blowing snow sublimation is an important physical process in the drifting snow.In previous studies,many researchers thought that the drifting snow sublimation near surface could be ignored,and they generally focus their attention on the sublimation of suspended particles.However,many studies have shown that the humidity in the salattion layer has not reached 100%,and the sublimation of the saltating particles still exists.Most previous studies on blowing snow assume that there is sufficient snow cover on the surface,and there is insufficient research on the characteristics of blowing snow under conditions of limited snow cover.Therefore,we developed a blowing model that contains the saltation and suspension.Based on this model,we studied the movement characteristics of the saltating and suspended snow particles in the blowing snow,and the sublimation of saltating and suspended snow particles,and blowing snow with limited surface snow cover.The main work is as follows:Firstly,we found a determination condition of saltation and suspension for blowing snow,and based on this condition a blowing snow model containing the saltation and suspension was developed,combined with the wind field model,Lagrangian particle tracking method,diffusion equation,etc..The results show that the threshold particle size is a suitable determination condition for the saltation and suspension.Second,using the blowing snow model established in this paper simulates drifting snow.The results show that the mass concentration of snow particles decreases with height;the mass of saltating snow particles is much larger than that of suspended snow particles;the change of snow particles size distribution has almost no effect on the movement of saltating particles,however,it has a great influence on the movement of suspended snow particles.Thirdly,we simulated the blowing snow sublimation.The results show that sublimation by blowing snow will change the temperature and humidity;the negative feedback effect of saltating particles sublimation is much greater than that of suspended particle sublimation;mass of snow sublimation in the saltation layer accounts for even more than half of the total,therefore,it can't be neglected;the increase of temperature will increase the saltating particles sublimation rate,but its effect on the suspended snow particles sublimation is very complicated;the impact of blowing snow sublimation on the jump snow particles is very weak,but it will reduce the suspended snow particles in the air.Finally,we simulate the snow sublimation under limited snow cover.The results show that suspended snow particles will be greatly weakened under the condition of limited surface snow cover,but due to the supplementation of saltation sublimation,the number of suspended particles in the air will still maintain a certain amount;due to the sublimation of the saltating snow particles,the mean particle size of the snow particles on the surface will continue to decrease.In summary,in this paper we established a blowing snow model that contains the saltation and suspension.Based on this model,we have conducted some research on blowing snow,and revealed some rules in the blowing snow which would help deepen people's understanding of blowing snow.