Rapid Intensification of Typhoon Chanthu (2021) induced by topographic effects of Taiwan

Typhoon Chanthu (2021) underwent a unique rapid intensification (RI) when it moved northward offshore east of Taiwan under a northerly vertical wind shear. The recirculating flow of Chanthu’s outer circulation around south Taiwan led to the observed stronger convection at the offshore side of the typhoon. A multi-resolution simulation of MPAS has successfully captured the RI of Chanthu and indicated no RI in the absence of Taiwan terrain. Sensitivity tests help to explore the role of terrain-induced recirculating flow in the induced RI. Based on the solution of the extended Sawyer–Eliassen (SE) equation, diabatic heating contributes the most to the lower-tropospheric eyewall spinup in the nonlinear simulation. Asymmetric convection is enhanced in downshear left quadrant by the strong convergence between the recirculating flow and the typhoon’s inner vortex, resulting in a stronger contribution to the spinup than in the other three quadrants. Such asymmetric convection configured at the offshore side of the inner typhoon provides the dynamic mechanism of Chanthu’s RI.