热力不均匀场对一次冰雹天气影响的诊断分析

Diagnostic Analysis of the Effect of Thermal Inhomogeneous Field on the Hail

将天津地面自动观测站资料与850 hPa以上北京探空资料结合,组成新的探空资料,对2008年8月27日凌晨发生在天津的一次冰雹过程进行了诊断分析。此次冰雹过程有两处降雹区,一处位于天津北部的蓟县山区,另一处位于临海的汉沽地区。通过对热力和动力对流参数的水平分布和逐时变化研究,结果表明:(1)各对流参数可以反映出强对流天气的中尺度分布特征,尤其是CAPE高值区和LI低值区与强对流天气的发生区域对应较好,这对局地强对流天气的短时临近预测具有一定指示意义,表明边界层内的热力、动力特征对强对流天气的发生具有重要作用。(2)汉沽地区热力参数CAPE(LI)随时间增大(减小),而蓟县地区热力参数的变化则相反,表明两地冰雹的成因存在较大差异,前者的热力作用显著,后者的热力作用则不显著。汉沽地区热力不均匀分布造成的次级环流和上升运动使水汽凝结并释放潜热,触发了冰雹的发生。蓟县山地的抬升作用,使东移系统的上升运动得到加强,触发了冰雹。

Using the new data which are combined by the data from Automatic Weather Stations（AWS） in Tianjin and the data above 850 hPa in Beijing,a hail case in Tianjing before dawn of 27 August 2008 is diagnostically analyzed.The hail is observed in two areas,in which is Jixian mountain,other is Hangu area that is near to the sea.Through the research on the thermal and dynamic parameters,the results show that：（1） Using the new sounding data,the calculated convective parameters can reflect the distribution of the characteristics of the severe mesoscale convective weather,especially,the high value area of CAPE and low value area of LI is well correspording to occurrence area of severe convective weather.Besides,it shows that the thermal and dynamic characteristics in the boundary layer are significant to the short-time nowcasting of the local severe convective weather.（2）The thermal parameters of CAPE（LI） in Hangu area are increasing（decreasing） with time and it is opposite to the phenomena in Jixian area.This phenomena show that there is more significant difference in the reasons of causing the hail between those two locations.The former is dominated by thermal effect while the latter is not.In Hangu area,the reason is that the inhomogeneous distribution of thermal effect causes secondary circulation and upward motion,so that water vapor condense and release the heat.Due to the uplift effect of Jixian mountain,the upward system of the eastward movement is strengthened to cause the hail.