Contributions of tropical waves to tropical cyclone genesis over the western North Pacific
The present study investigates the relationship between the tropical waves and the tropical cyclone (TC) genesis over the western North Pacific (WNP) for the period 1979–2011. Five wave types are considered in this study. It is shown that the TC genesis is strongly related to enhanced low-level vorticity and convection of tropical waves and significant difference are detected in the TC modulation by dynamic and thermodynamic components of the waves. More TCs tend to form in regions of waves with overlapping cyclonic vorticity and active convection. About 83.2% of TCs form within active phase of tropical waves, mainly in a single wave and two coexisting waves. Each wave type-related genesis accounts for about 30% of all TC geneses except for the Kelvin waves that account for only 25.2% of TC geneses. The number of each wave type-related TC genesis consistently varies seasonally with peak in the TC season (July-November), which is attributed to a combined effect of active wave probability and intensity change. The interannual variation in the TC genesis is well reproduced by the tropical wave-related TC genesis, especially in the region east of 150°E. An eastward extension of the enhanced monsoon trough coincides with increased tropical wave activity by accelerated wave-mean flow interaction.
KeywordsTropical cyclone genesis Tropical waves Western North Pacific
The first author would like to acknowledge the hospitality of Atmosphere and Ocean Research Institute, University of Tokyo, for providing the visiting researcher program. This research has benefited greatly from conversations with Prof. Renguang Wu, and Prof. Ronghui Huang. This work is jointly supported by the National Natural Science Foundation of China Grant 41475077, and 41461164005, and the National Basic Research Program of China under Grant 2014CB953902.
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Conflict of interest
The authors declare that they have no conflict of interest.
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