又称“对流不稳定（convective instability）”。整层空气上升达到饱和后，原有的稳定层结转化为不稳定层结。
对流层高层或平流层低层高位涡的下传有利于位势不稳定能量的释放，使得暴雨增幅。
The tropopause folding, which means that high PV spreads downward from the upper troposphere or stratosphere, helps the releasing of potential instability energy and the development of rainstorm.
锋面南方存在深厚的位势不稳定区域，一旦有抬升运动产生，便很容易激发出强烈的对流运动，从而产生强降水。
A deep area of potential instability existing on the south of front, intense convective motion and heavy rainfall will be aroused in the case of uplift.
低涡切变线、西南风低空急流、东风气流和地面倒槽是本次暴雨的主要影响系统，该地区维持高能，饱和，位势不稳定的小环境，有利于特大暴雨的产生和维持。
The following conclusions can be drawn. 1. The main influence systems of causing this heavy rainfall are southwest vortex, shear line and southwest low-level jet.
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