Katabatic Winds

Not all wind is driven by large-scale pressure systems or the rotation of the Earth. Katabatic winds form through a much simpler, local mechanism: gravity pulling dense, cold air downhill. The process begins when air near an elevated surface, such as a glacier, ice sheet, or a mountain slope at night, loses heat rapidly through radiation once the sun goes down. As that air cools, it becomes denser than the air surrounding it, and denser air is heavier for a given volume. Because the ground slopes downward, this heavy air doesn't just sit still -- it flows downhill under its own weight, essentially behaving like a slow-motion avalanche of cold air rather than a river of water. As the air descends, it can pick up considerable speed, particularly if it funnels through a narrow valley that concentrates the flow, similar to how a river speeds up when it passes through a narrow channel. Some of the strongest recorded katabatic winds occur along the coast of Antarctica, where cold air draining off the ice sheet's interior can reach hurricane-force speeds by the time it reaches the coastline. Unlike winds driven by large storm systems, katabatic winds are often most intense on clear, calm nights, since clear skies allow the surface to radiate heat away fastest, and the absence of larger competing wind patterns lets the gravity-driven flow dominate.