The Study of Inland Eyewall Reformation of Typhoon Fanapi (2010) Using Numerical Experiments and Vorticity Budget Analysis

Abstract

AbstractNumerical simulations of Typhoon Fanapi (2010) interacting with the terrain of Taiwan are conducted using the Advanced Research Weather Research and Forecasting model (ARW, version 3.3.1) on a triply nested grid (with the finest grid size of 1 km and 55 vertical levels). Fanapi made landfall on eastern Taiwan at 0000 UTC 19 September and left Taiwan at 1200 UTC 19 September 2010, producing heavy rainfall and severe floods. After landfall, the Fanapi eyewall weakened and broke down over the Central Mountain Range. Vortical hot towers (VHTs) occurred along the Fanapi rainband, and the VHTs in land have weaker maximum updrafts (7.0–8.0 m/s), narrower diameter (7.0–11.5 km), and shallower depth (6.5–9.0 km), compared with oceanic VHTs over the Taiwan Strait. The VHTs over the Taiwan Strait remained organized along the rainband and propagated toward the southeast quadrant of the Fanapi circulation over land by the tangential flow. These organized VHTs in the southeast quadrant help transport cyclonic vorticity from lower into middle levels and then cooperate with the rich vorticity within the rainband by horizontal vorticity advection to rebuild the Fanapi eyewall upward from the bottom. The vorticity balance within the entire Fanapi circulation is largely dominated by its southeast quadrant with organized VHTs over Taiwan Island. In the simulation with no latent heat release, the VHTs quickly decay and radiate outward from the eyewall as gravity‐wave perturbations.