湖南岳阳一次大暴雨过程近地层湍流特征分析

Analysis on the turbulence characteristics in near surface layer during a heavy rainstorm event in Yueyang of Hunan

利用杭瑞高速洞庭湖大桥测风塔上的三维超声风速仪观测资料以及岳阳气象站逐小时降水资料,分析了2016年7月3—5日湖南岳阳一次大暴雨过程的三个不同时段近地层湍流特征。结果表明:(1)强降水来临前180—230min和结束前10—50 min的近地层物理量场出现异常,且强降水来临前的物理量场异常出现时间较结束前早。风速、湍流强度、湍流动能在大暴雨过程中出现异常偏大,强降水来临前230 min,风速出现最大值4.875 m·s^(-1);强降水结束前50min,湍流强度出现最大值,水平纵向、水平横向、垂直向的湍流强度分别为1.255、1.173、0.195。(2)强降水来临前与结束前,湍流功率谱密度出现异常偏大。大暴雨过程中的湍流功率谱密度减小,湍流功率谱密度最大值的频率左移。(3)强降水来临前的湍涡尺度最大,强降水期间的湍涡尺度次之,强降水结束后的湍涡尺度在三者中最小,低频大涡为大暴雨过程中的湍流活动提供了能量。

Using the 3 D ultrasound anemometer data from wind measuring tower at Dongting Lake Bridge of Hangfeng highway and hourly precipitation at Yueyang weather station, several conclusions have been reached from the analysis of physical field characteristics in near surface layer during three different periods of a heavy rainstorm event from 3 to 5 July 2016. The results show that(1) the physical fields in near surface layer appeared abnormal within 180-230 minutes before the heavy rainfall and within 10-50 minutes before the end of the heavy rainfall. Comparing with the occurrence of anomalous features before the end of heavy rainfall, the occurrence of anomalous features before the heavy rainfall was earlier. During the heavy rainstorm event, wind speed, turbulence intensity and turbulent kinetic energy had large abnormal values, and at 230 minutes before the heavy rainfall, the wind speed appeared the max value of 4.875 m·s^(-1). At 50 minutes before the end of heavy rainfall, turbulence intensity showed the max value, turbulence intensity in the direction of horizontal downwind was 1.255, of horizontal crosswind was 1.173, of vertical was 0.195.(2) Before the onset and the end of the heavy rainfall, the PSD(Power Spectral Density) increased. The frequency of the highest value of PSD shifted to the left in the whole heavy rainfall event.(3) Compared to the scale of eddy during and after the heavy rainfall, the scale of eddy before the heavy rainfall was the largest one. The scale during the heavy rainfall was less than the one before, and the one after the heavy rainfall was the lowest among the three different periods. The large-scale eddy with low frequency had provided energy for the turbulent activity of the heavy rainstorm event.