东北冷涡暴雨的特点及其非对称结构特征

Asymmetric Characteristics of the Northeast Cold Vortex and Its Effect on Heavy Rain

以2009年6月8日个例为主,对东北冷涡造成的华北暴雨的卫星云图、雷达回波特征及降水特点进行了分析,并利用NCEP FNLs分析资料分析了东北冷涡的非对称结构特征、对流不稳定的建立过程和可能的释放机制。结果表明:东北冷涡具有非对称结构特征;除对流层中层风场、温度场结构较对称外,冷涡在对流层高层对应低槽、暖中心和高空急流,在对流层低层对应倒槽、暖舌,冷中心不明显;冷涡的负涡度、主要辐合辐散和上升运动中心分布在冷涡东南部;在冷涡东南部,对流层中层自西北伸向东南的干冷平流叠加在自西南伸向东北的暖湿平流上,造成对流不稳定迅速增长,且午后晴空辐射增温进一步加强了对流不稳定;冷涡系统建立对流不稳定的同时,冷涡东南部的上升运动为对流有效位能的释放提供了有利条件。

The characteristics of cloud image,radar image and precipitation during the heavy rains caused by the northeast cold vortex are analyzed using some cases including June 8,2009. Based on the NCEP FNLs analysis data,the three dimensional structure characteristics,the possible establishing process and releasing mechanism of convective instability are studied further. The results showthat the northeast cold vortex has dynamic and thermal asymmetric characteristics except for the middle layer of atmosphere. In the upper level troposphere the cold vortex evolves to a trough accompanied by a warm center and an upper- level jet stream,but in the lowlevel troposphere itturns to an inverted though and a warm tongue while the cold center is not obvious. The main negative vorticity,divergence and upward motion distribute in the south by east of the cold vortex. The dry and cold advection in the middle atmosphere superimposes on the low- level warm and moist advection in the southeast part of the rotating cold vortex,causing rapid growth of the convective instability which can be enhancedby the warming of surface air due to the net radiation in afternoon. While the cold vortex produces convective instability,the upward motion in its southeast part provides favorable triggering conditions leading to the convection development and the releasing of instable energy.