I've heard that if a cold air layer exists above a warm one, sound may be refracted upward, causing it to miss hearers that otherwise could hear the sound.
My understanding (which may not be correct) is that as the wave leaves the source, the top of the wave front encounters the cold air and starts slowing down. This drags the faster part of the wave toward itself (since it's going more slowly), eventually lifting the wave off the ground.
If this is so, I'm confused about why the wave hangs together. Why doesn't the bottom half of the wave front simply split away from the slower portion, and continue at normal speed and direction, reaching the hearers on the ground like normal? What "glue" holds the wave together, allowing the slower portion of the wave front to drag the faster portion upward?
Any help is appreciated.