Role of the Vertical Structure of a Simulated Tropical Cyclone in Its Motion: A Case Study of Typhoon Fengshen (2008)

抄録

Typhoon Fengshen (2008) was marked by a persistent track toward the northwest, which was poorly predicted by an operational hydrostatic model, which indicated a significant northward bias. Using a global nonhydrostatic model with finer grid spacing, we have simulated a reliable track of this typhoon. The purpose of this study is to clarify the causes of the northward bias by comparing the output of the two models. This typhoon was marked by the asymmetry of rainfall concentrating in the downshear side. While both models could reproduce the asymmetric structure, a significant difference between them was found in the vertical structure. In the hydrostatic model, the vortex tilted to the downshear side with a displacement from lower to upper levels exceeding 100 km. This tilt was related to weak updrafts of, at most, 0.5 m s⁻¹. Diagnosis using vorticity budget demonstrated that the tilt of the vortex resulted from a lack of vertical coupling that was too weak to withstand differential advection between the lower and upper levels. These results suggest the importance of reproducing inner-core updrafts for better track prediction of a typhoon in an environment with strong vertical shear.