台風同士の相対運動に対するモンスーントラフの影響

抄録

In this study, the effect of the zonally-elongating monsoon trough (MT) on the interaction of binary tropical cyclones (BTCs) is investigated by using data analysis and idealized simulations. The interaction of BTCs is found to be sensitive to the relative orientation of the two tropical cyclones (TCs) embedded in the MT. When the two cyclones are lined up in a northeast–southwest (NE–SW) orientation, the MT steers the two cyclones to approach each other and promotes the Fujiwhara effect. In contrast, when the initial cyclones are oriented in the northwest–southeast direction of the MT, they will move away from each other under the large-scale steering flows.

Idealized simulations are conducted to understand how the MT and the β-effect influence the BTC interactions, focusing on NE–SW oriented pairs. The steering flows at different stages are examined by partitioning them into the one from the MT and the other cyclone in the pair. The analysis shows that the binary TCs' motions are mainly controlled by the large-scale steering flows in the initial stage. In the case of BTCs with a NE–SW orientation, the MT can promote two TCs to approach each other, thus increasing the possibility of binary interactions.

The sensitivity of the interaction of BTCs to their intensities, the strength of the MT, and the β-effect are examined. The stronger the MT, the stronger its large-scale steering flows will be, thus making the two NE–SW oriented TCs merge faster. Furthermore, the binary interaction is stronger on the β-plane compared with that on the f-plane. It is likely due to the β-induced Rossby wave energy dispersion. As the MT evolves into a monsoon gyre (MG)-like pattern, a pronounced southwesterly flow emanates in the southeast quadrant of MG. This southwesterly flow acts as a steering flow to help the western TC move northeastward, accelerating to reach the critical distance.