Qingju, Yi (Chineese Academy of Meteorological Sciences, Beijing)
Yihui, Ding (National Climate Center, Beijing)
Xingde, Xu (Chineese Academy of Meteorological Sciences, Beijing)
Based on the surface maps, the extratropical cyclones over the East Coast of China have been investigated, 25% of them can develop into explosive cyclones. The most of the explosive cyclones belong to moderate intensity.
The secons part of the present paper has addressed the physical condition of explosive cyclogenesis. The diagnostic analysis has indicated that the thermal advection plays a significant triggering role for development of the cyclones at initial stage; the large scale heating is a primary factor favorable for rapid development of cyclones at latter stage. At the developing stage, Isentropic Potential Vorticity (IPV) systems at low and upper levels is adequately superposed in vertical, with the maximum IPV at high level. This contition is very favorable for baroclinic unstable development. The estimate of kinetic energy budget also indicates that close association of explosive development of cyclones with baroclinic development. In addition, the explosive development of cyclones often occur on the left quadrant of the exit region of upper-level jet streak. Finally, the numerical simulation has shown that the development of the rapidly deepening cyclones are closely related to atmospheric condensational heating, sensible heat flux and vertical distribution of water vapour turbulent flux. But, the deepening rate of the cyclone is dependent on the height of the maximum heating level.
The chain of the synoptic process which favours the explosive development of extratropical cyclones over the East Coast of China have been derived: (1) outbreaks of cold air or winter monsoon in East Asia; (2) the warm and moist air advection and the resulting frontogenesis along coastal areas, often accompained by the rapid development of a low-level jet stream; (3) cyclones move over the left quadrant of exit zone of the upper-level jet streak, (4) the condensation heating, baroclinic instability and the associated positive feedback, (5) the air-sea interaction processes and (6) explosive development cyclones. The comparing between the cyclones in the Mediterranean and the East Coast of China will be studied further.