Interactions between Typhoons Tembin (2012) and Bolaven (2012): Effects on the Unusual Looping Motion of Tembin

The interactions between typhoon Tembin (2012) and Bolaven (2012) are investigated using the Weather Research and Forecasting (WRF) model with a horizontal grid spacing of 10 km. Observed looping motion of Tembin and north-northwestward movements of Bolaven are reproduced in the numerical simulation. The interaction regime between Tembin and Bolaven is classified to “elastic interaction” in all time steps, and the centroid-relative tracks of two typhoons also show their mutual cyclonic rotations. Piecewise potential vorticity inversion technique is used to quantify the interaction between two typhoons, and new centroid-relative tracks are obtained by considering the magnitude of tangential velocity from the counterpart typhoon. The new centroid-relative tracks show that the looping motion of Tembin is dominated by the interaction with Bolaven while there is no significant effect of Temin on the movements of Bolaven. The effects of topography in Taiwan and large-scale forcing on the looping motion of Tembin are also investigated. The tracks of Tembin in the simulations with reduced terrain height are similar to that with original topography, which implies the unclear influence of topography. On the other hand, the North Pacific high in the south of Tembin develops rapidly, and strong westerly is formed due to the combination of Tembin's cyclonic circulation and anticyclonic flow from North Pacific high. This results in the increase in the asymmetry of flow near Tembin, and partly contributes to the looping motion of Tembin.