Temperature Inversions

We keep hearing about the inversion over Fairbanks. What is it?

Normally, the air near the ground is warmer than the air at higher altitude. An inversion is the reverse situation--colder air at ground level than higher up.

Cold air is heavier than warm air. Thus once an inversion forms, the air is very stable. Mixing that would normally occur by the rising of warm air is inhibited. Consequently pollutants such as carbon monoxide, sulfur compounds and ice fog remain trapped near the ground when there is an inversion.

Fairbanks has some of the world's strongest inversions, sometimes 30° to 40° F colder at ground than at several hundred feet above ground.