My thanks to George Bumann for sending over this great pic of a temperature inversion in Yellowstone Park.
During temperature inversions cool air becomes trapped under a layer of warmer air. It typically happens overnight under clear skies.
In this photo, steam is rising over Mammoth Hot Springs until it hits the top of the cool air layer. Regular readers will be aware that this is a sign that as well as temperature, sounds and smells will also have been affected.
In the inversion layer, sounds become trapped and travel further, meaning we can often hear things that are normally too far away. Smells also get trapped, mix and spread out, giving the air a signature musty smell.