Causes of windy weather in Tibet

(l) In the winter half year, two high-altitude jets in the westerly belt pass over the plateau. Because of its short distance, high intensity and low height, it is free to pass from west to east on the plateau. In addition, the turbulence disturbance caused by the air heating near the plateau during the day promotes the downward transport of the upper westerly jet momentum, resulting in an increase in the surface wind speed and a large-scale gale in the plateau. As long as there is a stable strong westerly jet over the plateau, there will be a strong wind blowing to the west, and the daily variation of the wind is obvious. Generally, the wind is very small in the morning and evening, and it increases sharply around noon.

(2) From L to April, there is strong warm air northward in the southern part of the plateau, and strong cold air invades in the northern part of the plateau, which is deadlocked over the central part of the plateau, forming an east-west strong front area and a strong jet. Lhasa is located on the warm air side of the strong front area, and the high-altitude wind speed is very high, and the momentum is transferred downwards, which makes the ground form a strong wind.

(3) In addition, the canyon effect of topography, mountain range and small topography is related to the generation and intensity of strong winds. For example, the northwest of Tibet has a high altitude and open terrain, and the trend of mountains is consistent with that of high-altitude rapids, so there is strong wind and strong wind. The altitude in southern Tibet is also high, and it is also easy to form strong winds due to the canyon effect. Due to the low altitude in the southeast of Tibet, the mountains run north-south, which is less affected by the high-altitude westerly jet and has less strong winds. Therefore, the occurrence of high winds in the plateau is not only related to the atmospheric circulation, but also related to the high temperature and low pressure characteristics of the plateau itself. This is related to windy winter and spring, strong solar radiation, sparse vegetation on the surface and complex terrain, which forms the characteristics that evaporation on the plateau is greater than precipitation. The higher the altitude, the lower the humidity and the drier the air. Absolute humidity (the weight of water vapor actually contained in one cubic meter of air, expressed in grams) and relative humidity (the ratio of absolute humidity to the maximum saturated humidity in air) are both low. Because of the low humidity, Lhasa at the same temperature is not as cold as Chengdu.