Analysis on Environmental Condition for Wind Gust in Beijing Area

Wind gust is caused by the convective cloud and is different from the tornado. Based on the rainfall, the wind gust events are divided into two kinds, i.e., the dry and the wet ones. The instability and environmental wind perpendicular distribution within the troposphere in the wind gust days are analysed respectively. The results indicate that the environmental condition is some different for these two kinds of events. In dry wind gust days, the value of convective available potential energy is very low but the vertical wind shear below 6 km is great. So, the dynamic instability due to the strong wind shear plays an important role in the convective development in these days. And the utilization of instability indexes in convection development forecast is restricted. However, the convection initiation causing the wet wind gust is easier for forecast because the environment is normally instable. Mainly, the difference in soundings leads to above dissimilarity. Therefore, the wind perpendicular distribution should be taken into consideration while making the wind gust potential forecasting. Most of the wind gust events (not only dry but also wet ones) develop when the downdraft convective available potential energy is higher than 600 J·kg-1 and the value increases before the strong wind approach, which is also useful. Prior to the wind gust, the environmental lapse rate of temperature below the lifting condensation level also rises obviously. Besides, the profiler data are supplementary to the sounding. In some events, the isotach in higher value goes down continuously and reaches the surface while the gust breaks out. If the profiler data could be used effectively, the nowcasting and warning for the wind gust might be improved.