Observational Investigation of a Tornadic Heavy Precipitation Supercell Storm

A detailed analysis of a tornadic heavy precipitation(HP) supercell's environmental conditions,structure and evolution is made based on the Doppler weather radar data,routine upper-air and surface observation,and intense automatic weather station observation.The main results are as follows: (1) This HP supercell occurs in the moderate convective available potential energy(CAPE) and significant vertical wind shear environment,with high value of low level vertical wind shear and low lifting condensation level(LCL) at the same time.The moderate CAPE and significant vertical wind shear favor the generation of supercell,while the high value of low level vertical wind shear and low LCL favor the occurrence of strong tornadoes.(2) This HP supercell begins to develop when the pre-existing long convective rainbelt widens and shortens,the mesocyclone first appears in the middle cell of the rainbelt,beginning at 4-km height and then developing upward and downward.Soon,the mesocyclone also develops in the southern cell of the rainbelt,and gradually the southern cell merges with the middle cell,forming a strong HP supercell,with a 12-km diameter and 9-km height mesocyclone embedded.The vertical vorticity associated with the mesocyclone is 1.5×10~(-2) s~(-1).The radar echo of this supercell successively displays kidney bean,spiral,S shapes,and finally evolves into bow echo,lasting more than 2 hours.(3) The F3 tornado occurs during the S shape period.Before tornado touches down,a tornado vortex signature(TVS) appears in the central part of the large mesocyclone,corresponding to a vertical vorticity value of 6.0×10~(-2) s~(-1).When the tornado is underway,strong divergence occurs at the storm top above the tornado,with a divergent value of 0.8×10~(-2) s~(-1).The mesocyclone that leads to the tornado lasts 2 hours and 13 minutes.The mechanisms for mesocyclone generation and HP echo revolution are discussed in details.