Observation of a Tornado in the Circulation Background of Northeast Cold Vortex

The synoptic situation and Doppler radar data of the tornado process of Taobei District of Baicheng city in Jilin Province on 12 June 2012 (referred as "612" tornado) are analyzed, results are as follows.The tornado process occurrs in the southeast quadrant of the upper cold vortex, and in the convective unstable region of the north of the upper-level jet and the left of the low-level jet, also, in a relatively warm and humid environment of the surface systems. The caculation of atmospheric convective parameters shows that strong vertical wind shear (no less than 6.0×10^-3 s^-1) occurs at low layer (0-1 km) and relatively low lifting condensation level (no more than 1 km) exists in the tornado process, and the convective available potential energy is large before the tornado occurs. As for the radar echo characteristics, the height of the strong core (no less than 50 dBZ) is below 4 km in the tornado event, making it a low centroid convective system. The tornado occurs in the strong echo zones where a banded echo with an approximate nodular echo join together, and it gradually evolves into an "S" type with "V" type gap, and the echo of the strongest center value reaches 61 dBZ. Using the Doppler radar derived products and the radial velocity map, tornado vortex signature (TVS) could be detected, indicating that "612" tornado occurs in strong convective storm with smaller-scale TVS and larger vertical vorticity (about 3.65×10^-2 s^-1-3.83×10^-2 s^-1), having short duration. TVS could be identified in advance before the tornado, so it is very useful for estimation and prediction of tornados.