Radar Observation of Boundary Layer Wind Structure Associated with Landfalling Typhoons in China

This study examines, for the first time, the characteristics and changes of boundary layer wind structure associated with five typhoons making landfall in South China using coastal operational radar. The volume velocity processing (VVP) method has been applied to derive the vertical wind profiles below 3 km. It is shown that VVP-derived winds are consistent and in good agreement with those from GTS soundings, with the mean error of the wind speed and direction being 1.m s-1 and 2 o respectively. Results show that the heights of the maximum total wind speed and the inflow layer depth, which are usually defined as the dynamic boundary heights, both decrease with decreasing radius to the storm center. The height of the maximum tangential wind speed is located at the height where the radial wind speed is 20% of the peak inflow. These features are consistent to previous studies on the boundary layer structure in tropical storms over open ocean and at landfall in America. Different from previously documented low-level jet which has been observed to be mostly pronounced in the eyewall, the wind profiles show distinct low-level jets in both the eyewall and primary rainband in this study. The wind speed maximum is located below 500 m and found to be 80~100% higher than the 3-km wind speed in eyewall. In contrast, the jet feature in the primary rainband is located at 1.5 km with the value of 20~40% greater than the 3-km wind speed.