Beijing Weather Forecast Centre
Affected by special geographical environment, winter snowfall in Beijing is often accompanied by easterly wind in boundary layer. The water vapor transport and dynamic convergence effect caused by wind in boundary layer easterly are of great significance to the occurrence and development of snowfall. Different from the existing snowfall studies on boundary layer easterly wind in plain areas, based on the topographic characteristics of Yanqing Zone of 2022 Winter Olympic Games, this paper compared the mechanism of easterly wind in boundary layer with different thermal and humidity properties and development heights on snowfall under similar weather conditions.The results show that: (1) A longer route through the Bohai Bay is beneficial to the obvious humidification of the boundary layer easterly wind, and vice versa. (2) The "dry and cold" easterly wind can form a cold pad to lift the warm and humid air in Beijing plain area. When the easterly wind develops deep in the vertical direction (over 600m), it can overturn Jundu Mountain with lower altitudes in eastern Yanqing and form a confluence on leeward slopes. At the same time, it is blocked Haituo Mountain with higher altitudes in the west, forming the forced uplift of the windward slope. The combined two effect leads to the convergence of the east is strong and the west is weak, which causes the distribution of snowfall is more east than west. (3) The "warm and humid" boundary layer easterly wind cannot cross Jundu Mountain westward due to its low vertical extension height, which has little effect on snow in Yanqing. (4) When the air is affected by the northwest airflow of 500hPa, closer to the terrain, the saturation area near the 700 hPa height and the lifting movement will make the high altitude mountain area of Yanqing experience obvious snowfall.