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

Using the 3D 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.