青奥开幕式期间南京地区浅层对流成因及逆向移动特征分析

Causes of Shallow Layer Convection and Characteristics of Its Reverse Move in Nanjing During Opening Ceremony of Youth Olympic Games

利用常规观测资料、加密自动站资料、多普勒雷达资料及NCEP 1°×1°再分析资料,针对第二届青年奥运会开幕式期间形成发展于对流层低层偏东气流中的对流引发南京局地短时强降水天气进行了分析,探讨了低层偏东气流中浅层弱对流的形成机制、降水期间伴随在降水云系中逆向移动的两类对流单体的雷达特征和移动原因。结果表明,降水期间,南京上空对流层低层维持偏东风,中层以上则为西南风,两者之间的过渡区对应一干层,该干层由对流层中层的一支偏北气流携至的干空气形成,叠置于对流层低层较浅薄偏东暖湿气流之上,促进了对流层中低层对流不稳定层结的发展。地面风场扰动形成的局地辐合及地面非锋性斜压带激发了对流层低层偏东气流中对流的形成。镶嵌于降水回波中逆向移动的两类对流单体结构差异明显,两类对流单体质心高度、垂直伸展厚度与所在高度层中所盛行的背景风场决定了对流单体的传播与移动。

Based on the conventional observation data,automatic station data,Doppler radar data and NCEP 1°×1° reanalysis data,the convection cells that formed and developed in the lower troposphere in the easterly airflow are analyzed and the local short-term severe precipitation in Nanjing during YOG（Youth Olympic Games） opening ceremony caused by the convection cells is also studied.Moreover,the formation mechanism of the convection in the shallow layer of the easterly airflow,the radar characteristics and the reasons of the convection cells reversely moving in the precipitation cloud system during the rainfall are discussed.The results show that the lower troposphere over Nanjing blows easterly wind while the middle-above layer is dominated by the southwesterly wind.The transition zone between them corresponds to a dry layer which was formed by dry air carried by a northerly air in the middle troposphere.The overlapping of the dry layer on the shallow easterly warm airflow promotes the development of the convective unstable stratification in the mid and low troposphere.Local convergence by the surface wind disturbance and surface non-frontogenesis baroclinic zone inspires the formation of the convection in the easterly airflow.The structures of the two kinds of reversely propagating convective cells in the precipitation echo have obvious differences.The barycenter height,vertical extension thickness and the prevailing background wind in the layer determine the propagation and movement of the convective cells.