Clarification of localized structure in gust hazard from the viewpoint of turbulent organzied motion

通过在水箱中滴下浓溶液来再现行进微暴流。用DPIV方法测量了它们的速度场。模拟微下击暴流的平均速度迹线与实际微下击暴流的平均速度迹线相似。湍流强度仅为峰值速度的10%。在多风扇风洞中得到的阵风锋水平速度场基本均匀。这些事实表明，由于大气边界层中的湍流脉动，局部风灾害不会发生。我们发现，当下沉气流不受周围涡的扰动而集中时，就会出现局部阵风。在平均风速为16 m/s的实际微下击暴流中，模拟的局部阵风风速为30 m/s。

Traveling microbursts were reproduced by dropping dense solution in a water tank. The velocity fields of them were measured through a DPIV method. Mean velocity trace of the simulated microbursts was similar to that of actual them. Turbulence intensity was only 10 % of the peak velocity. The horizontal velocity fields of gust front realized in the multifan wind tunnel were almost uniform. These facts show that localized wind hazards do not occur due to the turbulent fluctuation in atmospheric boundary layer. We found that the localized wind gust appeared when the downdraft was not disturbed by surrounding vortices and concentrated. The simulated localized wind gust was found to correspond to be 30 m/s in the actual microburst whose mean velocity is 16 m/s.