Whole process wind characteristics field measurements of typhoon Morakot

This paper presents field measurement results of boundary layer wind characteristics over typical open country during the passages of typhoon Morakot passed by Wenzhou in Aug. 2009. The field data such as wind speed and wind direction were measured from two propeller anemometers placed at the height of 30m. The measured wind data are analyzed to obtain the information on mean wind speed and direction, turbulence intensity, gust factor, turbulence integral length scale, spectra of wind speed fluctuations and co-coherence of measured wind data. The results clearly demonstrate that the turbulence intensity and gust factor of typhoon Morakot are larger than normal, and there is a tendency for the turbulence intensities to decrease with the increase of the mean wind speed, however, there is another tendency for the turbulence integral length scale to increase with the increase of the mean wind speed.The power spectral densities of fluctuating wind speed in longitudinal and lateral directions obtained from the measured wind speed data roughly fit with Von Karman spectra. The measured co-coherence is smaller than the exponential function calculated results recommended by Davenport, but is roughly consistent in the zero frequency point with the Shiotami empirical formula computed result.