page_title: Katabatic wind
section_title: Impacts
hierarchical_section_title: Katabatic wind / Impacts
caption_attribution_description: English: Sketch of the Antarctic coast with glaciological and oceanographic processes. Deutsch: Schematische Darstellung glaziologischer und ozeanographischer Prozesse an der Küste der Antarktis. Über dem antarktischen Eisschild fällt Niederschlag in Form von Schnee (Precipitation). Der Eisschild (Ice sheet) ist weitgehend am Untergrund festgefroren (back stress) und hat sich bis zu einer Mächtigkeit von über 4000 m aufgebaut. Das Eis fließt nach allen Seiten vom Kontinent ab, z.T. konzentriert in Eisströmen (Ice stream). An der Küste verliert das Eis im Bereich der Aufsetzlinie (Grounding line) den Kontakt zum Untergrund, wird deutlich dünner (einige 100 m) und bildet über dem Schelf (Continental shelf) ein Schelfeis (Ice shelf) = Eis, das noch mit dem Eisschild verbunden ist, aber bereits schwimmt. Fließt das Schelfeis über eine Untiefe, entstehen Eisrücken (Ice rise). An der Schelfeiskante brechen Tafeleisberge ab (Calving line, Iceberg calving), die auf ihrem Weg um die Antarktis in wärmerem Wasser schmelzen. Eine Küstenpolynya entsteht, wenn kalte ablandige Winde (Catabatic wind) das Meereis (Sea ice) von der Küste wegtreiben. In Verbindung mit der Neueisbildung entsteht kaltes, salzreiches und damit schweres Wasser, das den Kontinentalhang (Slope) herabfließt und den wesentlichen Mechanismus für die Bildung des ozeanischen Bodenwassers in der Tiefsee (Deep sea) darstellt.
context_page_description: A katabatic wind is 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; the spelling catabatic winds
  is also used. Katabatic winds can rush down elevated slopes at hurricane speeds, but most are not as intense as that, and many are 10 knots or less.
  Not all downslope winds are katabatic. For instance, winds such as the föhn and chinook 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. Examples of true katabatic winds include the bora in the Adriatic, the Bohemian Wind or Böhmwind in the Ore Mountains, the Santa Ana in southern California, the piteraq winds of Greenland, and the oroshi in Japan. Another example is "the Barber", an enhanced katabatic wind that blows over the town of Greymouth in New Zealand when there is a southeast flow over the South Island. "The Barber" has a local reputation for its coldness.
context_section_description: 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. Where these winds are concentrated into restricted areas in the coastal valleys, the winds blow well over hurricane force, reaching around 300 km/h (190 mph).  In Greenland these winds are called piteraq and are most intense whenever a low pressure area approaches the coast.
  In a few regions of continental Antarctica the snow is scoured away by the force of the katabatic winds, leading to "dry valleys" (or "Antarctic oases") such as the McMurdo Dry Valleys. Since the katabatic winds are descending, they tend to have a low relative humidity, which desiccates the region. Other regions may have a similar but lesser effect, leading to "blue ice" areas where the snow is removed and the surface ice sublimates, but is replenished by glacier flow from upstream.
  In the Fuegian Archipelago (Tierra del Fuego) in South America as well as in Alaska in North America, a wind known as a williwaw is a particular danger to harboring vessels. Williwaws originate in the snow and ice fields of the coastal mountains, and they can be faster than 120 knots (140 mph; 220 km/h).
caption: Coastal polynyas are produced in the Antarctic by katabatic winds
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