台风莫拉克 (0908) 影响期间近地层风特性

通过对台风莫拉克 (0908) 影响范围内的33座测风塔观测资料的分析可知:台风莫拉克越靠近陆地，风场的非对称性越明显，其行进方向的左侧测风塔风向呈逆时针旋转，右侧测风塔风向顺时针旋转。在远离台风莫拉克的地方风向稳定，湍流强度变化较平稳；在台风莫拉克登陆点附近，风向、风速和湍流强度均会出现突变。台风莫拉克影响期间，湍流强度与风速的关系未出现IEC标准曲线那样随风速增大稳定减小，其I₁₅达B级和A级及以上的平均湍流强度会在风速7~17 m·s-1形成一个峰值；无论南风或北风，风速越大，各层湍流强度差异趋于减小，同等风速、高度的湍流强度偏南大风均大于偏北大风。位于台风莫拉克登陆点北侧测风塔湍流强度随风速的增加先减小后增大，最终各高度全部超过IEC标准A级曲线，而位于南侧测风塔湍流强度随风速的变化比北侧小，并随风速增大趋于标准A级曲线；另外北侧测风塔湍流强度大于南侧，且各高度偏北大风湍流强度之间的差异比南侧相应风向明显，表明北侧垂直方向的扰动更强。台风莫拉克阵风系数为1.2~1.7，其随高度变化与地形有关，一般情况下随高度升高而减小，在复杂地形条件下不符合随高度升高减小的规律。

Wind Characteristics Study in Surface Layer of Typhoon Morakot(0908)

The observations from 33 anemometer tower within Typhoon Morakot (0908) affected area are analyzed. As the typhoon moves closer, the wind asymmetry becomes more apparent. Morakot has a counterclockwise shift of wind direction on the left flank, and a clockwise shift of wind direction on the other flank. Near the landing area, the wind reaches maximum and the direction is northerly before landing. When landing, the wind slows down, its direction rapidly changes and air pressure drops rapidly. Southerly gale appears when landing and northerly gale appears to the north of the location where it enters the sea.In the place far away from Morakot, wind direction is steady and the turbulence intensity changes are correspondingly stable. Its value is decided by sub-layer attribute, complex surface conditions lead to strong turbulence intensity.Near the landing area, the wind direction, the wind speed and the turbulence intensity may all changes suddenly. In the mountainous region, turbulence intensity change is most complex. Influenced by Morakot, the turbulence intensity curves do not look like the IEC standard curve which reduces stably along with the wind speed increasing. The turbulence intensity reaches a peak with wind speed of 7—17 m·s-1when I₁₅achieves Level A, B or above. No matter southerlies or northerlies, each layer turbulence intensity difference tends to reduces with wind speed. Given the same wind speed and height, the turbulence intensity of southerly gale is bigger than that of the northerly gale. Turbulence intensity decreases first then increases with wind speed increasing at Morakot landing area northern flank, finally surpassing IEC the standard Level A curve. But to the south of landing location, turbulence intensity along with the wind speed changes much smaller than the north side and increases along with the wind speed, showing the standard Level A curve tendency. On the north side turbulence intensity is bigger than the south side and at each height the turbulence intensity difference reduces remarkably compared to south side. It indicates that the north side vertical direction the perturbation is stronger.Morakot gust coefficient is between 1.2 and 1.7. The average gust coefficient changes with height and regional terrain, and it also becomes larger when the typhoon center draws near. In general cases, the gust coefficient reduces with height. But over complex terrain especially the knoll mountainous region it reduces with height below 50 meters, and increases with height above 50 meters.