Numerical Simulation of Falling-Snow Deposition Pattern Over 3D-Hill

Snow distribution over complex terrain is an important input quantity for hydrological modeling. Earlier numerical studies on falling-snow deposition pattern mostly focused on two-dimensional (2D) hills. This is simulated over a three-dimensional (3D) hill using a large-eddy simulation model. It is shown that for both 2D and 3D cases, the hill blocking effect leads to the formation of a snow accumulation zone on the windward slope. For the 3D case, the maximum snow deposition occurs on the leeward toe, but not for the 2D case under the same background conditions. The main reason for these differences is that the spanwise terrain change in the 3D case weakens this hill blocking effect and concurrently generates terrain-scale vortices which cause spatially variable snow depositions. It is found that an additional snow accumulation zone forms on the leeward slope of the 3D-hill due to the presence of a horseshoe vortex there. The low wind velocity regime bracketed by the vorticity streamers forms another large snow accumulation zone on the leeward toe. While the results here are only applicable to small hills in a mountain chain, they provide the necessary information for the parameterization of large-scale snow patterns for hydrological modeling. As snowflakes fall from sky, the trajectories of the snow particles would be influenced by the complex wind field near the undulant ground surface, and finally form uneven snow cover. Previous study about falling-snow deposition is mainly on two-dimensional hills (2D-hill). We simulated the wind field over a single three-dimensional hill (3D-hill), and mapped the falling-snow deposition pattern over the 3D-hill by tracking the snow particle movement. Based on the analysis of wind field characteristics and the snow particle movement, we found that the falling-snow deposition pattern over undulant terrain not only influenced by the mean flow but also the large vortex formed by the hill. There are three snow accumulation zones. The first one is on the windward slope forms by the blocking effect of the hill. The low wind speed at the leeward toe forms the second zone. A horseshoe vortex formed on the leeward slope forms the third zone. The maximum snow deposition is on the leeward toe for 3D-hill, while for 2D-hill it depends on the particle-flow conditions. This work could improve the accuracy of water balance study in mountain chains. Three snow deposition zones formed on the three-dimensional hill: on the windward slope, leeward toe and leeward slope, respectivelyDifferent from two-dimensional hill, the maximum snow deposition intensity is on the leeward toe for three-dimensional hillThe vorticity enhancement would result in the falling-snow deposition enhancement on the undulant terrain