From the synoptic point of view, the formation of gale is mainly caused by the strong cold air invasion, i.e. the cold front transit, the secondary circulation passing through the front, which causes the strong rise in front of the front and the momentum passing down behind the front, resulting in the variable pressure wind, which is the main factor causing the gale near the ground; the second is that the development of the surface hot low pressure before the cold front increases the pressure gradient in front of the front to form the gradient wind. Strong cold air is the driving force for the formation of dust weather. Only enough cold air can form a strong pressure difference and promote the horizontal flow of the atmosphere. At the same time, due to the different horizontal wind speed at different altitude and the strong convergence of the lower layer, the air is forced to flow in the vertical direction, resulting in strong horizontal and vertical movement. The maximum instantaneous wind speed is 17 meters per second, and the sandstorm can occur if the wind speed is above seven or eight levels in a short time. The intensity of cold air is stronger than that of normal gale.
大气层结是否稳定是形成沙尘暴的另一决定性因素。以最常出现区域性强沙尘暴的甘肃省河西地区为例,这里处在冷空气东南下的西北通道上,一般来说,冬春两季特别是春季经常有势力强大的冷空气入侵,而且春季植物稀少,沙漠和裸露的地表温度上升得很快,只要连续晴好两三天,地面气温可以升得很高。如果这时遇上强大的冷空气在中午前后过境,可形成上冷下暖的不稳定的温度层结,沙尘暴常常在此时发生。
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