The Impact of Taiwan Terrain on Tropical Cyclone Track

Both observational and numerical studies have shown that a tropical cyclone (TC) tends to deflect when approaching and passing over a mesoscale mountain range. The role of the terrain-induced channeling effect has been identified in our previous series of studies. In order to further understand the roles of orographic influence, idealized experiments are conducted in Weather Research and Forecasting (WRF) Model with 3-km horizontal resolution. Consistent with previous studies, the simulated west-moving TC shows pronounced southward track deflection when approaching the topography at certain flow regimes.

Deep layer mean advection (steering flow) calculated in the inner-core region of the TC aligns with the TC motion before landfall. Different from the mechanism related to the channeling-effect-induced low-level-jet as suggested in some previous studies, this study indicates that the leading role of the northerly asymmetric flow in the lower-middle levels in causing the southward deflection of the simulated TC track. This result suggests a different mechanism that contributes to the terrain-induced southward track deflection.

Potential vorticity tendency diagnosis can also grasp the southward deflection of the TC. Consistent with the concept of steering flow, horizontal advection contributes to the deflection of track significantly, while the role of vertical advection and diabatic heating is negligible. The southward advection flow in PV tendency appears at middle levels. The uncertainty of the calculation of PV tendency diagnosis is also discussed in this study. Work is ongoing to apply PV tendency diagnosis to investigate the topography-induced deflection of TC track under various flow regimes.