Study on Total Force Divergence Distribution and Evolution Features of Landfalling Typhoon Fanapi （1011）

Using high-resolution simulation data for the landfalling typhoon Fanapi（1011） and the total force divergence equation, the horizontal distribution and evolution of the total force divergence/convergence of Fanapi are diagnosed. The lifespan of Fanapi is divided into five stages, and the vertical integration of the total force divergence/convergence is then calculated. During the initial rapid intensification stage, a convergence zone of the total force appears. In the mature and vigorous period, the total force convergence area appears as a roughly circular shape with a radius of about 150 km centered on the typhoon location. The convergence intensity is strongest around the typhoon center and decreases outward. On the periphery of the convergence zone lies the divergence zone, appearing analogous to the spiral cloud bands with a width of about 200 km. The convergence intensity decreases gradually, and its maximum deviates from the typhoon center when Fanapi makes its first landfall and the symmetrical structure is destroyed. After the second landfall, the divergence region shrinks rapidly, whereas the convergence area is relatively significant. Throughout the life history of Fanapi, the average convergence intensity is generally higher than that of divergence and has a significant positive correlation with the typhoon intensity. In summary, a distinct signal of the total force divergence/convergence always accompanies typhoon circulation, and its evolution is also capable of identifying the development of the typhoon intensity and structure.