Ground and mesoscale analysis of a tornado and heavy rainfall and their radar echo characteristics in Yancheng

The tornado,short-term heavy precipitation and other convective weather in Yancheng City on 3 July 2006 are analyzed based on the data of dense surface automatic meteorological stations and Doppler weather radar.Results show that the weather background of the convective weather is Changjiang-Huaihe storm weather situation of the Meiyu,including the westerly trough eastward in upper levels,southwest jet stream in low-mid levels and strong convective instability.The development and maintenance of surface mesoscale vortex cause a continued strong upward motion for the convective weather.The tornado occurs in the large reflectivity gradient region in low-mid levels of the non-supercell storm,with a marked small scale vortex feature in the average radial velocity.In addition,three tropical systems in the western Pacific subtropical high and the ITCZ provide abundant moisture for the short-term heavy rainfall.There is a close relationship between the short-term heavy rainfall (occuring in a period of the increasing to the strongest,and to the beginning of decrease for the jet stream in low-mid levels) and the strong echo area larger than 50 dBZ.