Interaction of Typhoons with the Taiwan Orography. Part II: Continuous and Discontinuous Tracks across the Island

Abstract

Numerical model simulations of west-moving tropical cyclones approaching and crossing the Taiwan orography are shown to contain many of the observed surface features. Vortices tend to track continuously around the northern end of the island due to the deflection of the deep-layer mean flow, and the vortex circulation is modified less because the higher winds to the right of the center do not have a strong interaction with the barrier. Discontinuous tracks predominate for vortices approaching the central southern portions of the Taiwan orography. Severe distortions of the inner-core circulation occur, and the surface pressure and surface wind centers become decoupled and may be dissipated at different rates. Numerical sensitivity studies demonstrate that more intense and rapidly moving vortices are more like to cross directly over the barrier and thus maintain a continuous track. In one special case of a weak but fast-moving vortex approaching the southern end, the model simulates the existence of dual centers downstream. These numerical simulations indicate that vortex reorganization downstream may occur as a downward extension from the upper-level remnants of the typhoon or as an upward growth of a low-level secondary vortex. In the second type, a new low-level center that is separate from the original vortex or the terrain-induced pressure trough becomes the center about which the tropical cyclone reorganizes. Distinctions between the two types of secondary vortex developments would be obscurred without the high vertical and temporal resolution fields from the model simulation.