Then, the mesocyclone's lower part becomes tighter, increasing the speed of the wind.

接着，“中气旋” 靠下的部分会更紧绷，以此给风加速。

Outside, cool, dry, sinking air starts to wrap around the back of this mesocyclone, forming what's known as a rear flank downdraft.

外部那些又干又冷的下沉气体开始在 “中气旋” 后侧环绕，形成一个 “后侧下环流”。

This unusual scenario creates a stark temperature difference between the air inside the mesocyclone, and the air outside, building up a level of instability that allows a tornado to thrive.

这种特殊的情景使 “中气旋” 内外部的气体间产生了非常明显的温差，由此造成的更高一级的不稳定性使龙卷风更加猖狂。