Analysis on dynamic and thermal structure and development mechanism in a cold vortex over North China

Through analyses on the structure and evolution characteristics of cold vortex from June 22 to 30,2008,it was found that this cold vortex developed strongly,its center at 300 hPa was evident,it also had induced frontal cyclone on the ground.In the process from the development phase to the initial weakening stage,the entire troposphere consisted of positive vorticity,which spread from middle and high level to low level gradually.In the development stage,high-altitude westerly jet strengthened in the south of the cold vortex,the longitude direction wind distribution tended to become symmetry on the east and west sides,in the east and south a strong vertical ascending motion appeared.The center of the cold vortex was dry and cold,the intrusion of dry and cold northwest air in middle troposphere played an important role in further development of the cold vortex.In this process,continuous southeast water vapor stream was transported from the Bohai Sea to north China,the convergence of water vapor was limited on the east and west sides mainly.The daily change's activities of the cold air going to the south at the rear of the cold vortex were obvious.The cold air penetrated to Beijing,Tianjin and Hebei areas from ten to thirteen o'clock,maintained for 15-20 h.The dry and cold air at the rear of the cold vortex intruded southward and led to the severe convection.