Using the analyses of weather process of an heavy rainfall system, it is found that there is a mesoscale disturbance in the lower troposphere over Yangzi-Hwai valley.

通过一次江淮流域暴雨天气过程的分析，发现在对流层低层存在一种中间尺度扰动。

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The second-order shear of the basic flow represents an instable factor for the symmetric disturbance, and drives the unstable mesoscale disturbance to travel in the meridional direction;

基流二次切变对于中尺度对称扰动来说是一个不稳定因子，并且驱动不稳定的中尺度对称扰动在南北方向传播；

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Five sorts of the vertical structure of wind disturbance fields are discussed. Among them, the effect of middle-low level wind disturbances is the strongest in the formation of mesoscale low.

对五种不同垂直结构的风场扰动进行了实验，其中以中低层的风场扰动在中低压形成过程中的作用更显著。

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