87th AMS Annual Meeting

Monday, 15 January 2007
Climatology of sub-monthly wave patterns associated with tropical cyclone tracks over the East Asian monsoon area during July-August season
Exhibit Hall C (Henry B. Gonzalez Convention Center)
Ken-Chung Ko, National Kaohsiung Normal Univ., Kaohsiung, Taiwan; and H. H. Hsu
This study explores the sub-monthly circulation features in the western North Pacific during July and August. The sub-monthly wave-like pattern propagates northnorthwestward from the southeastern Philippine Sea to East China. The wavelength is about 4000 Km and the phase speed is about 5m/s. This feature fluctuates in a 10-25 day timescale with a spectral peak at 12.5 days. More than seventy percent of the chosen cases occur concurrently with recurving tropical cyclones, which propagate along with the wave-like pattern. Therefore, these recurving tropical cyclones are part of the wave-like pattern instead of isolated vortices. The wave-like pattern occurs in a large-scale flow characterized by an enhanced monsoon trough that extends eastward into the Philippine Sea, and a strong ridge protruding westward from the subtropical high. It is suggested that the cyclonic phase of the wave-like pattern provides a favorable environment for the genesis, growth, and propagation of the recurving tropical cyclones.

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