图片来源：央视网
Our final two cloud types will not help you predict the coming weather, but they do give a glimpse of the extraordinarily complicated motions of the atmosphere.
我们最后要说的两种云不能帮你预告天气，但是可以瞥见大气异常复杂的变化。
Smooth, lens-shaped Lenticular cloudsform as air is blown up and over a mountain range.
平滑的透镜形状的荚状云是空气膨胀时在山脉上方形成。
Once past the mountain, the air sinks back to its previous level. As it sinks, it warms and the cloud evaporates. But it can overshoot, in which case the air mass bobs back up allowing another Lenticular cloudto form.
一旦经过山脉，空气就缩回到原先的水平。空气收缩时会升温，云朵会蒸发。但如果收缩过了头，空气团就会回弹，形成另一朵荚状云。
This can lead to a string of clouds, extending some way beyond the mountain range. The interaction of wind with mountains and other surface features is one of the many details that have to be represented in computer simulators to get accurate predictions of the weather.
由此产生的一连串荚状云会延伸到山脉的另一边。风和山及其他地貌的相互作用是电脑模拟器需要考虑的众多细节之一，否则无法准确预测天气。
06
Kelvin-Helmholtz
开尔文-亥姆霍兹浪状云
图片来源：人民网
The Kelvin-Helmholtz cloudresembles a breaking ocean wave.
开尔文-亥姆霍兹浪状云就像被打碎的海浪。
When air masses at different heights move horizontally with different speeds, the situation becomes unstable. The boundary between the air masses begins to ripple, eventually forming larger waves.
当不同高度的空气团以不同速度横向移动时，情况就会变得不稳定起来。空气团的边界开始起波纹，最后形成更大波浪。
Kelvin-Helmholtz cloudsare rare, because we can only see this process taking place in the atmosphere if the lower air mass contains a cloud.
开尔文-亥姆霍兹浪状云很罕见，因为这一过程只有在低处空气团中有云时才会发生。
The cloud can then trace out the breaking waves, revealing the intricacy of the otherwise invisible motions above our heads.
从这种云展现的碎浪形状可以窥见我们头顶上原本看不见的微妙变化。
文字来源：中国日报网
图片来源：新华网、中国日报网、中国天气网、央视网、百度百科、人民网
编辑：刘尚静
