Analysis on the causes of a tornado in Nanxi, Changge of Henan province and the preliminary study on radar warning

Using conventional meteorological data，four elements automatic weather station data and Doppler radar data, a rare tornado process occurring on July 19, 2010 at the Nanxi town, in the eastern Changge was analyzed. In the paper, the application of Doppler radar for effective early warning the similar strong convective weather was discussed preliminarily. The results indicate that the tornado was caused by favorable circulation background, which produced by the coupled of middle level jets and convergence at middle and low layers, and divergence at high layer. The dew point front at middle and low layers and the zone of strong moisture gradient were the trigger mechanism of tornado. The tornado is generated in the moist air and close to the moist gradient area. Characteristics of this process are the lower height of meso-cyclone echo base, the height of severely shear and echo top descended, less azimuth direction and strong vertical wind shear etc before the occurrence of tornado. And the meso-cyclone indicator using tornado radar detection was summarized.