A katabatic wind (named from the

Greek Greek may refer to: Greece Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group. *Greek language, a branch of the Indo-European language family. **Proto-Greek language, the assumed last common ancestor ...

word κατάβασις ''

katabasis A katabasis or catabasis ( grc, κατάβασις, from "down" and "go") is a journey to the underworld. Its original sense is usually associated with Greek mythology and Classical mythology more broadly, where the protagonist visits the Gree ...

'', meaning "descending") is a drainage wind, a

wind Wind is the natural movement of air or other gases relative to a planet's surface. Winds occur on a range of scales, from thunderstorm flows lasting tens of minutes, to local breezes generated by heating of land surfaces and lasting a few ho ...

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 that intense and many are 10 knots (18 km/h) 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 Windward () and leeward () are terms used to describe the direction of the wind. Windward is ''upwind'' from the point of reference, i.e. towards the direction from which the wind is coming; leeward is ''downwind'' from the point of reference ...

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 is the Japanese term for a wind blowing strong down the slope of a mountain, occasionally as strong gusts of wind which can cause damage. ''Oroshi'' is a strong local wind across the Kanto Plain on the Pacific Ocean side of central Honshu. This t ...

in Japan. Another example is "the Barber", an enhanced katabatic wind that blows over the town of

Greymouth Greymouth () (Māori: ''Māwhera'') is the largest town in the West Coast region in the South Island of New Zealand, and the seat of the Grey District Council. The population of the whole Grey District is , which accounts for % of the West Coas ...

New Zealand New Zealand ( mi, Aotearoa ) is an island country in the southwestern Pacific Ocean. It consists of two main landmasses—the North Island () and the South Island ()—and over 700 smaller islands. It is the sixth-largest island count ...

when there is a southeast flow over the South Island. "The Barber" has a local reputation for its coldness.

Theory

A katabatic wind originates from radiational cooling of air atop a plateau, a mountain, glacier, or even a hill. Since the

density Density (volumetric mass density or specific mass) is the substance's mass per unit of volume. The symbol most often used for density is ''ρ'' (the lower case Greek letter rho), although the Latin letter ''D'' can also be used. Mathematical ...

air The atmosphere of Earth is the layer of gases, known collectively as air, retained by Earth's gravity that surrounds the planet and forms its planetary atmosphere. The atmosphere of Earth protects life on Earth by creating pressure allowing f ...

inversely proportional In mathematics, two sequences of numbers, often experimental data, are proportional or directly proportional if their corresponding elements have a constant ratio, which is called the coefficient of proportionality or proportionality constan ...

temperature Temperature is a physical quantity that expresses quantitatively the perceptions of hotness and coldness. Temperature is measurement, measured with a thermometer. Thermometers are calibrated in various Conversion of units of temperature, temp ...

, the air will flow downwards, warming approximately adiabatically as it descends. The temperature of the air 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 does not always) become hot by the time it reaches sea level. In Antarctica, by contrast, the wind is still intensely cold. The entire near-surface wind field over Antarctica is largely determined by the katabatic winds, particularly outside the summer season, except in coastal regions when storms may impose their own wind field.

Impacts

Katabatic winds are most commonly found blowing out from the large and elevated ice sheets of

Antarctica Antarctica () is Earth's southernmost and least-populated continent. Situated almost entirely south of the Antarctic Circle and surrounded by the Southern Ocean, it contains the geographic South Pole. Antarctica is the fifth-largest cont ...

and

Greenland Greenland ( kl, Kalaallit Nunaat, ; da, Grønland, ) is an island country in North America that is part of the Kingdom of Denmark. It is located between the Arctic and Atlantic oceans, east of the Canadian Arctic Archipelago. Greenland i ...

. 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 . 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 The McMurdo Dry Valleys are a row of largely snow-free valleys in Antarctica, located within Victoria Land west of McMurdo Sound. The Dry Valleys experience extremely low humidity and surrounding mountains prevent the flow of ice from nearby ...

. 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 Tierra del Fuego (, ; Spanish for "Land of the Fire", rarely also Fireland in English) is an archipelago off the southernmost tip of the South American mainland, across the Strait of Magellan. The archipelago consists of the main island, Isla ...

) 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 .Williwaw
''weatheronline.co.uk''. Accessed 2013-04-29. In California, strong katabatic wind events have been responsible for the explosive growth of many wildfires, including the 2018 Camp Fire and the 2020 North Complex.

References

External links

* {{Authority control Wind Climate of Antarctica Climate of Greenland

Theory

Impacts

See also

References

Further reading

External links