Abstract:
Typhoon Aere (2004) and Meari (2004) that formed in the western North Pacific in 2004 and tracked northwestward in a similar manner to each other until their tracks underwent changes over the East China Sea, where Aere (2004) moved southwestward and Meari (2004) took a sudden northeastward recurving track. This analysis shows that the interaction between low-frequency circulation and typhoons are mainly responsible for the track changes. As Aere (2004) was located to the south of the subtropical high, it interacted with the subtropical high through the advection of the low-frequency vorticity by synoptic-scale flows, enhancing negative vorticity on the northwestern side of the storm and thus the northeastward steering flow therein. Meanwhile, the Rossby wave energy dispersion strengthened the southwestward steering flows on the southeastern side of Aere. As a result, the synoptic-scale steering became weak, and Aere moved southwestward due mainly to the steering of the low-frequency circulation. On the other hand, Typhoon Meari gradually approached the western side of the subtropical high, and the synoptic-scale winds on the southeastern side of the typhoon was strengthened, which made Meari took a sudden northeastward track with no enhanced northeastward steering flows like the Aere case.