Katabatic wind
From Wikipedia, the free encyclopedia
A katabatic wind, from the Greek word katabatikos meaning "going downhill", is a wind that blows down a topographic incline such as a hill, mountain, or glacier. Such winds, particularly when they occur over a wide area, are sometimes called fall winds.
A distinction is drawn between winds that feel warmer than their surroundings (generally called Föhn or regionally, Chinook, Santa Ana, Bergwind or Diablo) and those that are cooler (for instance the Mistral in the Mediterranean, the Bora (or Bura) in the Adriatic or the Oroshi in Japan). In more recent times, however, the term katabatic wind usually refers to the cold variant.
The cold form of katabatic wind originates in a cooling, either radiatively or through vertical motion, of air at the top of the mountain, glacier, or hill. Since the density of air increases with lower temperature, the air will flow downwards, warming adiabatically as it descends, but still remaining relatively cold.
Cold katabatic winds are frequently found in the early hours of the night when the solar heating has ceased and the ground cools by emitting infrared radiation. Cold air from extratropical cyclones may contribute to this effect.
Over Antarctica and Greenland, prominent (although unnamed) cold katabatic winds exist, blowing for most of the year.
Winds which blow up a slope are called anabatic winds.
Katabatic winds are sometimes experienced by yachts at anchor. They often appear after a windless evening and arrive an hour or two after dark. They can blow very hard (up to gale force) for about an hour before dying away. This can be a frightening experience as the anchor may have been set with only the expectation of light winds and the yacht can easily have its anchor dragged. Katabatic winds can go up to 200 miles per hour.
[edit] References
- McKnight, TL & Hess, Darrel (2000). Katabatic Winds. In , Physical Geography: A Landscape Appreciation, pp. 131-2. Upper Saddle River, NJ: Prentice Hall. ISBN 0-13-020263-0
