1.National Climate Center of CMA;2.State Key Laboratory of Severe Weather,Chinese Academy of Meteorological Sciences of CMA
Based on the in-situ gradient observations from the wind profile radars, WindCubeV2 and masts during the landfall of Typhoon Minguk (1822) and Lekima (1909), combined with the simulated winds of typhoon Minguk (1822) with a finest horizontal resolution of 2 km and vertical resolution of 50-model levels, in which the lower levels are densified, the strong wind structure in the lower level (below 300 m height over sea level or terrain) were analyzed. It showed that within the range of 0-200 km from the typhoon center, (1) the maximum wind speed height and the wind shear index increased outward along the radial direction, and the wind shear index on the land underling surface was generally higher than 0.12. Because of the weak drag effect on the ocean underling surface, the wind shear index was usually small with the exception of island areas; (2) the strong wind shear on the right front quadrant of the moving direction of typhoon remained stable at about 0.17, which was not sensitive to distance and altitude. There existed the wind profile similar to the jet stream on the left rear quadrant, and previous study pointed out that the changes of super-gradient/ sub-gradient wind in the vertical direction should be responsible for the jet type profiles (Tan et al., 2013). The vertical variations of the strong winds on the left front quadrant showed nonlinear characteristics, indicating the more complex strong wind structure over this area; (3) the gust factor and turbulence intensity decreased with the mean wind speed and altitude; (4) the maximum wind direction variation during the landfall of typhoon decreased outward along the radial direction, and exhibited statistically significant spatial asymmetry with the largest variation near the right rear quadrant. Over some areas of the right rear quadrant, the wind direction changed more than 30° in half an hour, and most of them occurred before or during the typhoon"s landfall. It was hoped that these information could be helpful for microscale wind simulation as well as the prevention and mitigation of typhoon disasters over offshore wind farms in China.