When there's a deep melting layer followed by a little sliver of sub-freezing air at the surface, you'll get freezing rain.

当地表有一个深层的融化层，然后表面上有一些低于冰点的空气时，你就会看到冻雨。

If an ice shelf had very unhealthy firn layers, or the melting firn layers, you may not be able to see these things.

如果冰架雪层十分不坚固，融化现象严重的话，就不会有唱歌的现象发生。