Outbreak of Hazardous Local Gusts by Interactions of Gradient of Potential Temperature near the Ground with Surrounding Terrain Effect

本文通过一些观测实例和数值模拟，研究了近地位温梯度和周围地形形态的相互作用如何影响阵风的发展，并注意了台风通过时山脊上的强风在山脚附近变得更强的现象。(1)安装在风洞底板的冷却箱，结合用热丝加热接近气流上层的装置，可以使小型风洞中接近气流的温度梯度更大。(2)一些风洞试验表明，温度梯度（即大气的稳定性）强烈地影响了二维山地模型背风附近大风区的生长。(3)在具有v型山谷的二维山地模型中，一些风洞试验表明，与二维山地模型相比，大风区的产生不同。(4)利用几种商用软件对有山谷的山脊线风场进行了参数化研究，结果表明，模拟的大风区位置与风洞试验结果吻合较好。(5) 2004年，佐贺县Ogi市距离23号台风路径不小于300km，但风灾主要集中在该地区。数值模拟分析表明，位于Ogi市迎风方向的1000米高山上的一个浅山谷对该地区强风的加速有很强的影响。此外，计算的初始条件（风速入流条件）采用了实际气象观测资料，模拟结果与现场观测风速更加接近。(6)然而，我认为目前的数值模拟技术很难实现包含阵风高频分量的瞬时风速的精确再现。对于实际峰值阵风的预测，需要进一步创新的风流模拟。(7)同样，1998年3月福冈市西部地区一次局地大风爆发的参数化研究结果表明，除周围地形效应外，利用弗劳德数约为1.6的势温梯度可以较好地再现该地区阵风的发展。少

Our study showed how the interaction of the gradient of potential temperature near the ground and the configuration of surrounding terrain affects the development of a stronger wind gust using some observation examples and numerical simulation and paying attention to the phenomenon in which the strong wind running over a ridge during a typhoon passage becomes stronger near the foot of a mountain.(1)A cooling box mounted in a floor of a wind tunnel could make a stronger temperature gradient of an approaching flow in a small wind tunnel by combining a device which heats an upper layer of an approaching air by a hot wire.(2)Some wind tunnel tests showed that a temperature gradient, i.e., stability of atmospheric air, affected strongly the growth of a strong wind region near the leeward foot of a two-dimensional mountain model.(3)In the case of the two-dimensional mountain model which has a V-shaped valley, some wind tunnel tests showed the generation of the strong wind region different fr … More om the two-dimensional mountain model.(4)A parametric study on the wind flow over the mountain ridge line with a valley by several commercially available software shows that the locations of the simulated strong wind regions were in good agreement with the wind-tunnel-test result.(5)Although Ogi City in Saga Prefecture was no less than 300km away from the course of Typhoon No.23 in 2004, the big wind damage concentrated in the area. Some analyses by our numerical simulation indicated that a shallow valley in a 1000-meter high mountain which is located in a windward of Ogi City had affected strongly the acceleration of the strong winds in the area. Moreover, the simulation results became more similar to the observed wind speed at the site by taking in the data of actual aerologic observation data for the initial condition (wind-speed inflow conditions) of the calculation.(6)I think, however, the present numerical-simulation technique is difficult to realize precise reproduction of the instantaneous wind speed containing high-frequency components of gust. For forecasting of actual peak gusts, the further creative ingenuity of wind flow simulation is required.(7)Similarly as a result of parametric study of outbreak of a strong local wind seen at the western Fukuoka City area in March, 1998, it turned out that the development of the strong gust in this region can be better reproduced by operating the gradient of potential temperature with Froude number of about 1.6 in addition to the surrounding terrain effect. Less