Idealized simulations of the effect of Taiwan and Philippines topographies on tropical cyclone tracks

Abstract

The effects of topography on tropical cyclone (TC) tracks are investigated using the Weather Research and Forecasting model running on a beta plane with actual topography. Two sets of experiments are performed, one focusing on Taiwan topography and the other on the Philippines. In each set, different parts of the terrain are set to be either present or absent and the TCs are inserted at a location southeast of the mountain so that landfall occurs at the central part of the mountain in the no-terrain (control) cases. Relative to the control case, a pair of terrain-induced gyres is found in all with-terrain experiments. This pair of gyres rotates cyclonically around the TC and the gyre-associated flow near the TC centre causes a northward deflection of the TC track prior to landfall. An examination of the potential vorticity tendencies (PVTs) suggests that, in addition to the PVT produced by this flow, the PVT from diabatic heating cannot be ignored in explaining the TC track during landfall. The asymmetric diabatic heating is significant, which tends to retard the fast displacement of the TC caused by horizontal advection. This diabatic heating distribution results from three different mechanisms: an incursion of dry air from the mountain, low-level convergence induced by the terrain-altered wind field in the southwestern part of the TC and the development of convergence cyclonically inward from the eastern side of the mountain to the TC core. However, the first two mechanisms are apparently missing in the Philippine experiments because of the lower height and the moister air over the mountains on Luzon Island.

Idealized simulations of the effect of Taiwan topography on the tracks of tropical cyclones with different steering flow strengths

“…This is the fourth part, following Tang and Chan (, , ) (Parts I, II and III respectively), that investigates the effect of the Central Mountain Range (CMR) of Taiwan on the track of tropical cyclones (TCs) with different sizes (in term of radius of 15 m s −1 wind) under different strengths of easterly steering flow. Three different initial sizes (600, 350 and 250 km denoted as large, medium and small TC respectively) and three different strengths of steering flow (0, 5 and 10 m s −1 denoted as without, weak and strong steering flow respectively) are used in this study.…”

“…Tang and Chan (, hereafter Part I) identified several mechanisms for the track changes when a TC approaches a mountain. A pair of terrain‐induced gyres in the low to mid‐levels is generated over the Central Mountain Range (CMR) on Taiwan and mountains on Luzon (Philippines).…”

Influence of Mesoscale Topography on Tropical Cyclone Tracks: Further Examination of the Channeling Effect

“…Numerical simulation studies on the terrain-induced TC track deflection, a useful approach if with proper design, can be classified into studies of real cases (e.g., Wu 2001;Jian and Wu 2008;Huang et al 2011) and idealized experiments (Chang 1982;Bender et al 1987;Yeh and Elsberry 1993;Lin et al 1999;Wu and Kuo 1999;Kuo et al 2001;Lin et al 2005;Lin and Savage 2011;Huang et al 2011;Hsu et al 2013;Tang and Chan 2013). Numerical simulations with idealized settings, used in many previous studies, have provided insights into the terrain-induced changes in TC movement under different flow and parameter regimes.…”

Idealized simulations of the effect of Taiwan topography on the tracks of tropical cyclones with different sizes

“…Tang and Chan (, hereafter Part 1) found that a pair of terrain‐induced gyres is generated when a topography is embedded in the TC circulation. Negative vorticity is generated by the flow being forced to move upward on the upwind side of the mountain and eventually an anticyclonic gyre is generated.…”