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

Observations have documented typhoons experiencing pronounced track deflection before making landfall in Taiwan. In this study, idealized full-physics model experiments are conducted to assess the orographic influence on tropical cyclone (TC) track. An intense and westward-moving TC is simulated to approach the bell-shaped terrain imitating the Taiwan topography. Sensitivity numerical experiments are carried out to evaluate the topographic effect under different flow regimes and parameters, such as TC intensity, terrain height, and incident angle of the TC movement toward the topography. All the presented simulated storms experience southward track deflection prior to landfall. Different from the mechanism related to the channeling-effect-induced low-level northerly jet as suggested in previous studies, this study indicates the leading role of the northerly asymmetric flow in the midtroposphere in causing the southward deflection of the simulated TC tracks. The midtropospheric northerly asymmetric flow forms as a result of the wind speeds restrained east of the storm center and winds enhanced/maintained west of the storm center. In all, this study highlights a new mechanism that contributes to the terrain-induced southward track deflection in addition to the traditional channeling effect.