Statistical Characteristics of Wind Field Structures of Tropical Cyclones over the Western North Pacific Based on MTCSWA Data

On the basis of the MTCSWA (Multiplatform Tropical Cyclone Surface Winds Analysis) data, the climatic statistical characteristics of tropical cyclones (TCs) at different sizes, the variation of the averaged radial extent of different significant wind speed thresholds (i.e., 34, 50, and 65 kt, 1 kt≈0.514 m/s) in different quadrants, and the axisymmetricity of the radial extent of different wind speed thresholds and their correlation with TC intensity over the western North Pacific from 2007 to 2016 are investigated. In this study, the size and intensity of TCs are defined as the azimuthally averaged radius at which wind speed decreases to 34 kt (≈17.5 m/s) from the center and the maximum sustained winds near the TC center, respectively. The mean size of TCs over the western North Pacific Ocean is 221.9 km, with small TCs of 96.4 km and large TCs of 346.4 km. The activity location of large TCs is more concentrated, with a more northward distribution, than that of small TCs. The peak value of the mean size of all TCs occurs in August and October. The mean values of the azimuthally averaged radial extents of the 34, 50, and 65 kt wind speed thresholds are 221.9, 121.0, and 77.4 km, respectively. According to the definition of axisymmetricity, the radial extent of the 34 kt wind speed threshold has the lowest axisymmetricity and the 65 kt wind speed threshold has the highest axisymmetricity. Positive correlations exist between the radial extents of the 34, 50, and 65 kt wind speed thresholds and the TC intensity during the TC’s lifetime, among which the correlation between the radial extent of the 65 kt wind speed threshold and the TC intensity is the lowest. For a certain wind speed threshold, the correlation between its radial extent and TC intensity varies in different quadrants at different stages of the TC’s lifetime. The higher the wind speed is, the weaker the correlation between the axisymmetricity of its radial extent and TC intensity. Only the axisymmetricity of the radial extent of the 34 kt wind speed threshold shows a weak positive correlation with TC intensity during the TC’s lifetime.