Abstract:As cyclone is vortex, the parameter relative vorticity (for brevity, vorticity) can be used to exactly describe the position and intensity of extratropical cyclone. Thus, the research of the extratropical cyclone development is actually the mechanism analysis of vorticity. With the geostrophic wind vorticity at 1000 hPa adopted in this study, a typical extratropical cyclone with a spiral track occurred during 6-10 June 2014 is diagnosed using conventional observations and NCEP 1°×1° reanalysis data. Based on Petterssen’s equation, and the configuration of positive vorticity advection and divergence at 300 hPa and thermal advection at 850 hPa, this paper investigates the contributions of thermal advection in middle lower layer of troposphere, the vorticity advection at 500 hPa and the divergence induced by the vorticity advection at 300 hPa to the development of surface cyclone. The results show that: (1) Vorticity transferred between 2 positive vorticity zones at 300 hPa and 500 hPa. The first positive vorticity zone was the main one during cyclogenesis and development while the other became dominant in the decaying period. (2) In the whole troposphere, the vorticity centers moved cyclonically on a curve path. During the development of the surface cyclone, the positive vorticity centers tilted rearward with height, and while weakening, they were vertically overlapped at different levels. (3) The temperature advection played a major role in cyclogenesis while positive vorticity advection at 500 hPa was the main factor in the cyclonic development. (4) Cyclone would develop when the divergence caused by positive vorticity advection at 300 hPa was located above the frontal zone at 850 hPa.