Field measurement and analysis of turbulence coherence for Typhoon Nuri at Macao Friendship Bridge

For the purpose of investigating the turbulent and spatial coherent characteristics of strong wind during typhoon landing period, two 3-dimensional ultrasonic anemometer stations were set up 30 m horizontally apart on the Macao Friendship Bridge to caputure the turbulent wind velocities of Typhoon Nuri. Based on the reliable and representative field measured data, the mean wind speed and direction, turbulence intensity, turbulence integral scale, turbulence power spectra, spatial correlation coefficient and coherence function were statistically evaluated. The field measurement analysis have presented the following results: 1) Two anemometer stations provided consistent results. The mean wind speed variation in time domain presented typical M-shape curves. The strong wind (10-minute mean wind speed higher than 8th grade in Beaufort wind scale) direction changed in a big range up to 122-degrees-angle, indicating the field measurements scoped over the typhoon landing period. 2) The ratio of the longitudinal, lateral and vertical turbulence intensities of the strong wind in the typhoon eye wall region was 1:0.96:0.36. Compared with the code defined ratio 1:0.88:0.5, the lateral component was larger and the vertical component was smaller. 3) The value of integral scale increased when the eye wall of Typhoon Nuri passed over the field measurement site. Before the center of Typhoon Nuri arrived, the integral scale of the strong typhoon wind was about twice compared with that for the non-typhoon wind. 4) The spatial correlation of the turbulent wind, coherence function curve and the decay factor had significant differences at different times during the typhoon process. In the eye wall of the typhoon, the horizontal spatial correlation was relatively strong and horizontally spatial correlation spectrum decayed slower with frequency increase. The minimum regressed coefficient C in coherence function model was 4.67, which is lower than the code defined low limit. The maximum decay factor was 27.75 which is larger than the code defined upper bound. The strong wind characteristic parameters of Typhoon Nuri mentioned above partly represented the turbulent and spatial coherent characteristic during strong typhoon wind period.