To analyze the short-term change of the intensity and the moving track and speed of the vortex in the deformation field, an interaction index of vortex and deformation field (VDI) was presented. The background pattern of a heavy rainfall event caused by a tropical depression (TD) during 5-6 August 2001 was analyzed with a digital filter compositing method based on Lanczos window function. It is shown that a col field forms as the strong Western Pacific subtropical high is splitting over eastern China. The TD intensifies as it is moving into the col field. Because the higher VDI which is favor of the development of TD represents the stronger interaction of the TD and the col field, the TD may move toward the high VDI region , so the VDI center can be taken as an indication of the moving direction of the TD. Furthermore, the distance between the TD center and the VDI center is also an indication of the moving speed of the TD. The bigger the size of distance, the quicker the TD moves.%为了分析涡旋在变形场中的短期强度、移动路径和速度的变化,提出了一个涡旋与变形场的相互作用指数VDI(interaction index of vortex and deformation field),采用基于Lanczos窗口函数的数字滤波合成分析方法,分析了2001年8月5、6日造成上海特大暴雨的热带低压(TD)过程的背景形势场及TD和VDI的关系.结果表明:强大的西太平洋副热带高压断裂,在华东沿海形成鞍型场,TD进入鞍型场后与其发生相互作用而加强.VDI值越大,越有利于TD的发展,TD将向VDI大值区移动,VDI的中心位置可以作为TD未来短期移动方向的指示.
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