Katabatic wind

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Coastal polynyas are produced in the Antarctic by katabatic winds

Katabatic wind spilling off an ice shelf

A katabatic wind, from the Greek word katabatikos meaning "going downhill", is the technical name for a drainage wind, a wind that carries high density air from a higher elevation down a slope under the force of gravity. Such winds are sometimes also called fall winds.

Not all downslope winds are katabatic. For instance, winds such as the foehn, Chinook or Bergwind, are rain shadow winds where air driven upslope on the windward side of a mountain range drops its moisture and descends leeward drier and warmer.

Katabatic winds can rush down elevated slopes at hurricane speeds, but most are not that intense and many are on the order of 10 knots or less.

Examples of true katabatic winds include the Mistral in the Mediterranean, the Bora (or Bura) in the Adriatic, the Santa Ana in southern California, and the Oroshi in Japan.

A katabatic wind originates from the cooling by radiation of air atop a plateau, a mountain, glacier, or even a hill. Since the density of air increases with lower temperature, the air will flow downwards, warming adiabatically as it descends. The temperature of the wind depends on the temperature in the source region and the amount of descent. In the case of the Santa Ana, for example, the wind can (but not always) become hot by the time it reaches sea level. In the case of Antarctica, by contrast, the wind is intensely cold.

Katabatic winds are most commonly found blowing out from the large and elevated ice sheets of Antarctica and Greenland. The buildup of high density cold air over the ice sheets and the elevation of the ice sheets brings into play enormous gravitational energy, propelling the winds well over hurricane force. In Greenland these winds are called Pitaraq and are most intense whenever a low pressure area approaches the coast.

In the Fuegian Archipelago (or Tierra del Fuego ) in South America as well as in Alaska, a wind known as a williwaw is a particular danger to harbouring vessels. It originates in the snow and ice fields of the coastal mountains. Williwaws commonly blow as high as 100 knots, and 200 knot williwaws have been reported. ^[1]

[edit] References

^ Dallas Murphy, "Rounding the Horn" (New York: Phoenix Books, 2004), p. 221.

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