This image taken by the crew of the International Space Station on August 20, 2003, illustrates how smoke has become trapped in valleys. Normally air temperature decreases with altitude; in other words, the higher up you are, the colder it is. Warmer, more buoyant air near the surface of the Earth usually rises into the atmosphere, carrying away air pollutants such as smoke. However, sometimes the “higher equals colder” relationship breaks down, for example, here in the northern Rockies, where light winds and cold air drainage from the higher elevations have created “temperature inversions,” making the air in the valley colder and denser than the air at the mountain peaks.
Published Sep 24, 2003