Influence of Topography on Tropical Cyclone Track – Idealized Simulations and Dual-Doppler Radar Analysis

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 terrain-induced channeling effect has been identified in our previous series of studies. In addition to conducting further idealized numerical simulations, in this work, the 3-D wind field derived from the dual-Doppler radar observations for 7 typhoons (Sinlaku, Krosa, Saola, Haitang, Talim, Jangmi and Fanapi) with deflected track as they approached Taiwan are also analyzed. The results show that during the looping motion of Typhoon Sinlaku, the wind is strengthened (weakened) in the western (eastern) side of Sinlaku in the midlevel due to the enhanced (restrained) vertical transport of tangential wind on the western (eastern) side of the typhoon. Such asymmetric distribution of tangential winds would lead to the southward steering flow near the TC-core and contribute to the southward deflection. This finding is consistent with our previous numerical studies.

In addition, the role of convective heating, induced by the orographic effect, in the TC track deflection during the passage, is also investigated by performing idealized experiments with specific designs in a full-physics model with 3-km horizontal resolution. Potential vorticity tendency analysis is also conducted to examine the factors leading to the storm's southward deflection near the terrain. These results will be delivered in our presentation.