有限区域分解分析方法在2006年一次东北冷涡暴雨分析中的应用

2006年7月19—24日,东北地区出现一次明显的冷涡发展导致强降水的过程.对这次东北冷涡过程的天气形势分析表明,该东北冷涡的维持和发展与冷涡东部阻塞高压的建立与消亡有关.本文根据500 hPa环流形势演变特征,将东北冷涡发生发展过程分为4个阶段,并借助调和-余弦谱展开方法,对东北冷涡各阶段850 hPa水平风和水汽通量进行无辐散和无旋转分量分解,分析各阶段无旋转风动能和无辐散风动能之间的能量转化.研究结果表明,分解得到的无辐散风及其水汽通量清楚地展现出了东北冷涡的大尺度环流和水汽输送通道及水汽来源,而从无旋转风及其水汽通量上则可以直观地看到冷涡低层的中小尺度风场及水汽辐合辐散区,为分析东北冷涡内部对流提供帮助.东北冷涡发展的不同阶段其水汽来源有所不同,初始阶段的水汽主要来自黄海和渤海地区,发展阶段水汽主要来自日本海,而到成熟阶段和减弱阶段,水汽输送通道被破坏,冷涡的水汽供应大大减少,与同时期暴雨减弱一致.同时,无旋转风辐合强值区和无旋转风水汽通量大值区的重合区域有利于强对流的发生发展,表现为重合区与TBB(Temperature of Black Body,黑体辐射温度)强对流云带的形状和位置对应良好,与降水落区也较为一致,可为预报东北冷涡引发的强降水落区这一预报难点问题提供参考.从动能转化上看,无旋转风和无辐散风的动能转化项能很好地反映东北冷涡整个生命史过程中各阶段强度的变化特点,对冷涡强度预报具有一定的指示意义.

The application of wind and water-vapor flux partitioning technique to the structure of a northeast vortex in 2006

A northeast vortex event happened during 19^th to 24^th July 2006 in northeast China; the event resulted in heavy rainfall in that area. From the weather situation of the northeast vortex, the maintenance and development of the vortex had strong connection with the buildup and breakdown of blocking high in the east. In the article, the northeast vortex event has been divided into four stages, resorting to the method of harmonic-cosine spectrum expansion, the horizontal wind and water vapor flux have been decomposed into two parts, the results indicate that, on one hand, from the nondivergent wind and its water vapor flux, the large scale circulation and vapor transportation passage have been exhibited intuitively, which can distinguish the source of water obviously, on the other hand, from the irrotational wind component and its corresponding water vapor flux, the convergence and divergence of meso-scale wind and water vapor can be seen directly, moreover, the overlap areas of convergence of strong irrotational wind and the large value of its water vapor flux correspond well to the strong convective cloud and the rainfall areas, therefore, it can be a useful help for the operational precipitation prediction of northeast vortex. From the kinetic energy of nondivergent wind and irrotational wind, the conversion term can well depict the trend of strength during the life cycle of northeast vortex.