云南一次切变线上中尺度低涡扰动的结构分析

Structure Analysis of Meso-α-Scale Low Vorticeson Shear Line in Yunnan

利用η中尺度数值模式模拟的时空高分辨输出、常规资料、GMS红外云图及TBB资料,对2002年6月25日切变线上中α尺度低涡扰动的结构、形成过程及冷空气来源进行研究,结果表明,低涡环流的尺度属于中α尺度,持续时间7小时左右,低涡成熟阶段,700hPa正涡度中心与低涡环流中心相重合,低空急流及强辐合中心位于低涡的东南象限;低涡环流由三股气流构成;低涡区上空存在超强散度柱、倾斜涡柱、深厚的上升运动区及特强垂直上升运动,超强散度柱与特强垂直上升运动互耦,强辐合、辐散中心发生在南、北风辐合、辐散且有强的v分量垂直梯度处,低层正涡度中心的上方,存在一负涡度中心;最大的水汽辐合位于700hPa及550hPa;低涡区冷空气来自500hPa的滇缅高压;大暴雨中心位于低涡中心的东侧。

The outputs of the η mesoscale numerical simulation, the observational data, the infrared cloud image from GMS and the TBB data are employed to study the structure and formation of a low vortex on the shear line and the sources of the cold air. The results show that the low vortex in this process belongs to the meso-α scale, with 7-hour duration. In the mature phase, the center of the positive vorticity is coincident with that of the vortex, and the 700hPa low-level jet and the strong convergent center located in its southeast quadrant. The vortex circulation is made up of three currents, with the super-strong divergence column, the vertical vorticity column, and the deep ascending motion region above. The deep ascending motion is coupled with the strong divergence. The centers of the strong convergence （divergence） emerged at the positions of the convergence （divergence） of southerly and northerly, accompanying with the strong vertical shear of meridional wind. In addition, there is a negative vorticity center over the low-level positive vorticity center. It is also found that the maximum vapor convergence located at 700hPa and 550hPa and that the cold air is mainly derived from the high over Yunnan to Burma at the 500hPa.