THE CONTRASTIVE ANALYSIS OF SYNOPTIC SITUATION AND DOPPLER RADAR DATA FOR TWO INTENSE TORNADO CASES

Two F2～F3 tornadoes,which occurred on 30 July 2005 in Lingbi and on 8 July in Wuwei,respectively,brought serious disaster to Anhui Province and greatly influenced the society.By analyzing the synoptic situation and Doppler radar data,it is found that the two cases have the same characteristics in synoptic situation.They both happened where there were high-level troughs and shears with warm,moist atmosphere on the surface,boundary-layer convergence line(such as cold front or thunderstorm outflow boundary etc) where tornadoes happened,and large low-level vertical wind shear.However,the difference between the two cases is that for Lingbi the vertical wind shear(VWS) is large at the 0～1 km low level but is small on the 0～6 km deep layer;for Wuwei VWS is large at both the 0～6 km and 0～1 km levels.With comprehensive analysis,the result displays that vertical wind shear has an important effect on the organization and maintenance of convective systems when CAPE exceeds a threshold.The radar base reflectivity factors of the two tornadoes are different from classical supercells,and the shape,intensity,and height of the echos are also different.But strong mesocyclone appeared in both tornado events and all the strong mesocyclone cores located at the lowest detectable height of radar.Vertical vortex of mesocyclone in the two tornadoes is about 2～6 mesocyclone units(one mesocyclone unit is 10-2 s-1),and vertical vortex on 8 July 2003 is greater than that on 30 July 2005.Radar-derived products,such as products of mesocyclone,are very useful to detect strong convective weather,Especially,the appearance of mesocyclone is half an hour earlier than that of tornado,which is quite important for tornado warning.