However, experts now know they are caused by planes moving through altocumulus clouds. Seen from below, the clouds can look like a large circle has been cut neatly from the clouds, with feathery ...

它们有时会形成一种特殊的图案，叫做高积卷云（Altocumulus castellanus），就像一座座小城堡一样耸立在天空中。 高层云（Altostratus）：这种云是由 ...