A Numerical Study on the Interaction of Binary Tropical Cyclones

The interaction of binary tropical cyclones (TC) is examined by conducting numerical simulations with idealized binary vortices in a β-plane using the Weather Research and Forecasting (WRF) model. Relatively high resolution simulations in a wide single domain with a horizontal grid spacing of 10 km are conducted by 144 hours integration to represent realistic dynamic as well as thermodynamic processes of each TC and their interactions. In a simulation with a separation distance of 640 km, two TCs show mutual cyclonic circulations, and the interaction regime is categorized into mostly the “elastic interaction” regime based on the Dritschel and Waugh's (1992) criterion during their evolution, mainly due to the separation distance of two TCs, except for at the final stage when the regime is changed to “partial straining-out” by increase in the vortex size of two TCs. The separation distance of two TCs increases up to 880 km until 84 hours, and then no significant variation occurs afterword. The eastern TC moves faster than the western TC by northward tangential velocity from the western TC, while its intensity is weaker than the western TC by the stronger vertical wind shear induced by faster transitional speed. This result is somewhat different from a previous study with the same separation distance, which was categorized into a "partial merger". This difference is likely due to that more realistic dynamic and thermodynamic processes of the two TCs, especially for intensity of TCs, and their interaction can be captured from the present simulation with much finer model resolution as well as improved model physics. In a simulation with a separation distance of 1440 km, no significant interaction between the two TCs occurs and the interaction regime is categorized into “elastic interaction, as in the previous low-resolution simulation. Sensitivity of the binary TC's interaction to the background wind and temperature, especially in the upper troposphere and lower stratosphere (UTLS), will be presented in the conference.