Abstract: Using the data of comprehensive observations from weather stations and the NCEP reanalysis data, circulation features and increasing process of explosive cyclone resulted in a snowstorm on November 25, 2013 over Heilongjiang province were analyzed.On this basis, distribution characteristics and vertical structure of vorticity advection and upper and lower jet were studied, so is the contribution of vorticity advection, positive and baroclinic of moist potential vorticity (MPV) to explosive cyclone.Dynamic mechanism of this explosive cyclone was discussed.The results show that cyclone center is under the positive vorticity advection zone in front of upper trough for this event.The positive vorticity convection makes isobaric surface reduced, thus cyclone maintains and develops.The surface cyclone is always located on the left front of the South upper jet core and the right rear of the North upper jet core.The dynamic effects of the two upper jets cause strong divergence in high troposphere.The coupling of high-low jet induces high divergence area overlaying on the top of low convergence area, which consequently leads to intense ascending movement.Thus, it increases intensity of cyclone development and snowfall.Strong baroclinicity is favorable to development of explosive cyclone.The burst of the cyclone is closely associated with the distribution and evolution of the moist potential vorticity.The downward spread of high MPV from the upper troposphere is also of an advantage to the cyclone development.When the equal ξ_mpv1 curve of the upper troposphere tends to quasi level condition, the cyclone gradually weakens.Increased atmospheric moist baroclinity can lead to increase vertical vorticity significantly, which accelerates development of explosive cyclone.The change of vertical vorticity is lagged behind wet baroclinicity.

Key words: Explosive cyclone, Moist potential vorticity, Coupling, Secondary circulation