温帯低気圧化の指標としての熱帯低気圧の発生過程に関する研究

抄録

A significant fraction of tropical cyclones develop in baroclinic environments, following tropical cyclogenesis “pathways” that are characterized by dynamical processes often associated with mid-latitudes. This study investigates whether such storms are more likely to undergo subsequent extratropical transition than those that develop in more typical, non-baroclinic environments. We consider tropical cyclones globally in the period of 1979–2011 using best-track datasets and define the genesis pathway of each storm using McTaggart-Cowan's classification: non-baroclinic, low-level baroclinic, trough-induced, and weak and strong tropical transition. In each basin, we analyze the total number and the fraction of storms that underwent extratropical transition as well as their seasonality and storm tracks according to their genesis pathways. The relationship between the pathways and extratropical transition is statistically significant in the North Atlantic and Western North Pacific, where the strong tropical transition and the trough-induced pathways have a significantly greater extratropical fraction compared with all other pathways, respectively. Latitude, longitude, and environmental factors, such as sea surface temperature and vertical shear, were further analyzed to explore whether storms in these pathways occur in environments conducive to extratropical transition, or whether a “memory” of the genesis pathway persists throughout the storm life cycle. After controlling for genesis latitude, the relationship between the strong tropical transition and trough-induced pathways and the extratropical transition occurrence remains statistically significant, implying a lasting effect from the pathway on the probability of an eventual extratropical transition.