多单体强风暴影响下的一次强降水超级单体演变特征分析OA北大核心CSTPCD

Based on the Tianjin Doppler radar data,conventional observation,ground automatic station me-teorological data,ERA5 reanalysis data and VDRAS data,a rare heavy precipitation(HP)supercell storm which was guided by a multi-cell strong storm occurred in the east of Hebei Province on 19 June 2017.In this paper,the evolution characteristics and maintenance mechanism of this supercell storm are mainly ana-lyzed.The results indicate that the sea breeze front and the gust front of the multi-cell strong storm,the tongue-shaped high temperature and high humidity area in the lower layer provided better thermal and dy-namic conditions for the formation of the supercell.When the convection cell moved into the tongue area,it rapidly developed into a supercell and moved southeastward along the outflow boundary of multi-cell strong storm.The relatively stable gust front fed by the slowly weakening severe thunderstorm not only provided long-time dynamic conditions for the development and maintenance of supercell,but also guided its movement.This is of great significance for the short-time and nowcasting of convective weather.At the beginning of the formation of supercell,affected by the outflow of multi-cell strong storm cold pool,the southerly winds near the ground turned to stronger easterly winds,changing the configuration of mesoscale environment significantly.The vertical wind shear of 0-6 km increased to 27 m·s-1 and the shear of 0-3 km increased to 17-19 m·s-1,which was the main reason for the rapid formation of meso-cyclone.The strong vertical vorticity advection on the convergence line was also conducive to the formation and maintenance of mesocyclone.The reason why the cyclone in supercell started at the lower level is that the vertical wind shear of 0-3 km obtained from VDRAS data was always about 20 m·s-1,the baroclinic vortex effect was obvious,providing a large and long-time horizontal vorticity input for the development and maintenance of supercell.During the formation and development of supercell,the storm relative helicity(SRH)was between 140 m2·s-2 and 171 m2·s-2,and exceeded 150 m2·s-2 for most of the time.Before the formation of supercell and near the dissipation stage,the SRH was significantly less than 150 m2·s-2.This indicates the SRH has a clear indication for the occurrence and development of supercell.The outflow of the cold pool preceded the formation of the supercell,strengthening the convergence and uplift of the in-flow.This was conducive to the development and maintenance of the supercell.In addition,there were more cells splitting from parent storm,which to some extent weakened the strong development of the su-percell,but it just made the sinking outflow not too strong but made the gust front move away quickly,causing the cold pool always to keep a certain intensity.At the same time,the front of multi-cell storm provided a stable vertical wind shear of 0-3 km(maintained at about 20 m·s-1)for the supercell.This resulted in a long-time balance between the wind shear and the strength of the cold pool,and finally made supercell maintain a stable state for a long time.In a word,the main reason why the supercell maintained self-organization for a long time is that the appropriate vertical wind shear provided by the mesoscale envir-onment kept balance with the development of the storm.