It's composed entirely of ice crystals cascading from the upper reaches of the troposphere, and as these ice crystals fall, they pass through different layers with different winds and they speed up and slow down, giving the cloud these brush-stroked appearances, these brush-stroke forms known as fall streaks.
它完全是由从上面的对流层 级联下来的冰晶组成， 当这些冰晶下落的时候， 它们穿过带有不同的风力的各个大气层 然后它们或加速或减速， 让这片云有了画笔刷过的图案， 这些图案形式被称作“雨幡”。