Abstract
We study the phenomenon of rapid cyclogenesis by examining the time evolution of the synoptic-scale environment for the 36-h period prior to most rapid intensification. We perform this study with the construction of composites for eight explosively-developing cyclones whose maximum intensification commences within a 5° latitude-longitude region in the vicinity of the Kuroshio Current. A comparison is made with corresponding composites of eight weakly-developing lows within the same region. The set of 16 cases is a comprehensive sample of events for nine cold seasons. Synoptic-scale features for the strong cases, distinct from those of the weaker cases, are detected throughout the 36-h dynamical conditioning period.
The stronger cases form to the south and west of Japan with antecedent propagation predominately over the maritime environment. The weaker systems, in contrast, either form in situ in our study region, or travel eastward from the Sea of Japan over the Island of Honshu. The unique thermodynamic precursors of the stronger systems include: a warm 1000-500hPa thickness anomaly that travels from the East China Sea northeastward into the Kuroshio region, and a cold thickness anomaly and thermal jet east of our study area. The dynamical consequence of the warm anomaly includes the development of an anomalous southwesterly thermal wind to the northwest where incipient surface development occurs.
We examine a representative strong case in which initial surface development occurs to the northwest of the warm anomaly in a zone of quasi-geostrophic forcing for ascent. The system subsequently propagates into a favorable location for further development downstream of a second 500hPa trough within the northwesterly polar jet. At the onset of explosive deepening, the cyclone is propagating towards a second region of anomalously cold air and strong baroclinity.
