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

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.