Analysis on Weather Process of Classic Supercell Storm in Northern Part of Fujian on 5 March 2010

A severe convective weather occurred in northern Fujian from 16:20 to 19:50 on 5 March 2010 was mainly caused by three local severe storms in mesoscale convective echo group.The strongest cell of three local server stroms was a classic(CL) supercell storm,which produced sever hail in 220 km along the way.Using radar data of Jianyang CINRAD/SA,routine upper-air and surface observation data,the CL supercell's evolving feature and environmental conditions were analyzed.The main results are as follows:(1)The storm appeared in a mesoscale low pressure which had the characteristic of the terrain occlusion in surface.The low pressure was in the front of the upper-troposphere trough,under the southwest middle-level jet,on the south side of shear-line and frontal zone on 850 hPa and in the front of low-level jet;the storm was produced from the cold front which located on the west of the low pressure,then the storm moved along the concentrated line in surface and passed through the center of the low pressure,at last the storm reached cold zone of stationary front which located on the east of the low pressure and quickly weakened then.The storm always maintained the relative isolated state and life-history was 4 h 52 min,the storm's average speed was 75 km·h-1 and the storm was a high centroid convective system.(2) During the mature stage(15:57-18:47) the storm maintained the classic supercell characteristics of the moderate intensity or more mesocyclone,the correlative bounded weak echo regions(BWER),lower-level hook-echo and other features.Moreover it come through three times peak development(16:03-16:34,16:52-17:17,17:41-18:47,respectively);correspondingly,the mesocyclone of the storm enhanced and stretched to the ground in the peak period.In the second peak period,the storm appeared the phenomenon of declining of echo-overhang,updating lower level hook-echo and disappearing of BWER,these evolving features were in accordance with the model of tornado-arising supercell.Moreover,in the second peak period the characteristic of the TVS further indicated the produced possibility of tornad to be large.In the third peak period the storm came up the similar evolving feature but the more typical is the mesocyclone came to occlusion at last,and then the storm formed vortex-echo which lasted half hour.Besides,in the first and the second peak period the gust-front-echo appeared in the left front of the storm several times rather than right-backward,which was favorable for lasting of the storm.(3) The main characteristics of storm-scale environment were the medium CAPE(Convective Available Potential Energy,1 685 J·kg-1),significant vertical wind shear(39 m·s-1,over 0~6 km),strong storm-relative inflow velocity(17 m·s-1,over 0~2 km) and strong storm-relative helicity(418 m2·s-2,over 0~2 km).However,Wind direction veered with altitude(90 °,below 300 hPa) was not only on low-level but also on middle-upper-level(25 °,over 500~300 hPa),which was certain different to those of CL supercell previously observed in middle latitudes.At lest,the mechanisms of three times peak development of the storm in the mature stage was also discussed.