thumb|270px|The causes of the Foehn effect in the lee of mountains (adapted from:)

thumb|260px|Dissolving [[Föhn clouds over Cumbre Nueva, La Palma, at an elevation of ]]

A Foehn, or Föhn (; , , ), is a type of dry, relatively warm downslope wind in the lee of a mountain range. It is a rain shadow wind that results from the subsequent adiabatic warming of air that has dropped most of its moisture on windward slopes (see orographic lift). As a consequence of the different adiabatic lapse rates of moist and dry air, the air on the leeward slopes becomes warmer than equivalent elevations on the windward slopes.

Foehn winds can raise temperatures by as much as in just a matter of hours. Switzerland, southern Germany, and Austria have a warmer climate due to the Foehn, as moist winds off the Mediterranean Sea blow over the Alps.

Etymology

The name Foehn (, ) arose in the Alpine region. Originating from Latin , a mild west wind of which Favonius was the Roman personification and probably transmitted by or just , the term was adopted as . In the Southern Alps, the phenomenon is known as but also and in Serbo-Croatian and Slovene. The German word (pronounced the same way) also means 'hairdryer', while the word is a genericized trademark today owned by AEG. The form phon is used in French-speaking parts of Switzerland as well as in Northern Italy.

The name was originally used to refer to the south wind which blows during the winter months and brings thaw conditions to the northern side of the Alps. Because Föhn later became a generic term that was extended to other mountain ranges around the world that experience similar phenomena, the name "Alpine föhn" () was coined for the Föhns of the Alpine region.

Causes

thumb|upright=1.5|The warm moist air from northern Italy is blocked on the [[windward side, loses much of its water vapor content, and descends on the French plateau and valley of the Mont-Cenis range in the Maurienne valley.]]

There are four known causes of the Foehn warming and drying effect.

Foehn winds are notorious among mountaineers in the Alps, especially those climbing the Eiger, for whom the winds add further difficulty in ascending an already difficult peak.

They are also associated with the rapid spread of wildfires, making some regions which experience these winds particularly fire-prone.

Purported physiological effects

Anecdotally, residents in areas of frequent Foehn winds have reported experiencing a variety of illnesses ranging from migraines to psychosis. The first clinical review of these effects was published by the Austrian physician Anton Czermak in the 19th century. A study by the Ludwig-Maximilians-Universität München found that suicide and accidents increased by 10 percent during Foehn winds in Central Europe. The causation of Föhnkrankheit (English: Foehn-sickness) is unproven. Labels for preparations of aspirin combined with caffeine, codeine and the like will sometimes include Föhnkrankheit among the indications. Evidence for effects from Chinook winds remains anecdotal, as it does for New Zealand's Nor'wester.

In some regions, Foehn winds are associated with causing circulatory problems, headaches, or similar ailments. Researchers have found, however, the Foehn wind's warm temperature to be beneficial to humans in most situations, and have theorized that the reported negative effects may be a result of secondary factors, such as changes in the electrical field or in the ion state of the atmosphere, the wind's relatively low humidity, or the generally unpleasant sensation of being in an environment with strong and gusty winds. which can be unusual compared to other Foehn winds in that the relative humidity typically changes little due to the increased moisture in the source air mass

  • Mono winds in the Sierra Nevada.
  • The Santa Ana winds of southern California, including the Sundowner winds of Santa Barbara, are in some ways similar to the Föhn, but originate in dry deserts as a katabatic wind. However, traditional Föhn conditions frequently prevail along the Santa Monica and Santa Ana Mountains and their respective leeward valleys, the San Fernando Valley and the Riverside County portion of the Inland Empire region.
  • Puelche wind in Chile
  • Suêtes on the west coast of Cape Breton Island, Nova Scotia, Canada
  • Wreckhouse winds in the southwest corner of the island of Newfoundland, Newfoundland and Labrador, Canada
  • Zonda winds in Argentina

;in Antarctica

  • Föhn wall on Signy Island, South Orkneys

;in Asia

  • Garmesh, Garmij, Garmbaad (): (, ) in Gilan region (near the Alborz) in the south west of Caspian Sea in Iran.
  • In winter, a Foehn effect occurs in the West Azerbaijan province, Iran (around Lake Urmia) as manifested by the province's dry winters relative to those in the windward part of the region (Northern Iraq or Kurdistan Province and Hakkâri Province in Turkey). For example, the winter rainfall of Urmia and Salmas in Iranian Azerbaijan is much lower than Batifa and Soran in Iraqi Kurdistan, and Hakkâri in the Hakkâri Province, which are roughly on the same latitude but are on the windward side of the Zagros Mountains.
  • Loo in Indo-Gangetic Plain
  • Warm Braw in the Schouten Islands north of West Papua, Indonesia.
  • Wuhan in China is famously known as one of the Three Furnaces on account of its extremely hot weather in summer resulting from the adiabatic warming effect created by mountains further south.
  • Laos wind (), hot-dry west wind () in northern and central Vietnam.

;in Europe

thumb|Foehn clouds upon the [[Karawanken mountain range, Carinthia, Austria]]

thumb|Foehn clouds over [[La Palma, Spain]]

  • Favonio in Ticino and north-western Italy due to western and northern winds crossing the Alps (mostly in winter)
  • Garbino in the Adriatic coast of Italy due to south-western winds crossing the Apennine Mountains (mostly in fall and winter)
  • Fen in northwest Slovenia
  • Fønvind in South Norway, in particular Central Norway, resulting in extreme winter warming, including Scandinavia's warmest winter temperature in Sunndalsøra.
  • Fogony in the Catalan Pyrenees
  • Föhn or Foehn in Austria, southern Germany, Switzerland, France and Liechtenstein
  • Föhn in Ostrobothnia and Western Lapland in Finland as moist air crosses Scandinavian Mountains and dries up.
  • Halny in the Carpathian Mountains, southern Poland and northern Slovakia
  • The Helm Wind, on the Pennines in the Eden Valley, Cumbria, England
  • Hnjúkaþeyr in Icelandic
  • Lodos wind, causing warm temperatures in the leeward side of mountains in the mild-winter climate of the Aegean Sea, Greece and western Turkey, as well as unusually mild temperatures in the cool or moderately cold winter climates north of the Marmara Sea, such as Istanbul, Adapazarı and Zonguldak.
  • Košava (Koshava) wind in Serbia that blows along the river Danube
  • Nortada in Cascais, and most notoriously in Guincho Beach, making it one of the best windsurfing spots in Europe
  • Ponentà in Valencia (eastern Spain)
  • Terral in Málaga (southern Spain)
  • Viento del Sur (Southern Wind) or Hego haizea in Basque in the Cantabrian region (northern Spain)

;in Oceania

  • The Great Dividing foehn in southeast Australia, leeward of the Great Dividing Range, observed in the coastal plains of New South Wales, and also in eastern Victoria and eastern Tasmania.
  • The Nor'wester in Hawkes Bay, Canterbury, and Otago, New Zealand

<gallery widths="180px" class="center">

File:Pájara Morro Jable - Carretera Punta de Jandía - cemetery + foehn 01 ies.jpg|Foehn over Carretera Punta de Jandía in Morro Jable, Pájara, Fuerteventura, Canary Islands

File:La Palma - El Paso - Cumbre Nueva+Foehn (Mirador Llano del Jable) 01 ies.jpg|Dissolving clouds from Foehn wind over the Cumbre Nueva in El Paso, La Palma, Canary Island

File:Wolkenwasserfall ms1408101.jpg|Foehn over Llano del Jable

File:Storm Oratia 30 Oct 2000.jpg|Foehn can be initiated when deep low-pressure systems move into Europe, drawing moist Mediterranean air over the Alps.

</gallery>

See also

  • Alpine climate
  • Anabatic wind
  • Chinook wind
  • Föhn cloud
  • Katabatic winds
  • Lee wave
  • Meteorology

References

  • McKnight, TL & Hess, Darrel (2000). "Foehn/Chinook Winds". In Physical Geography: A Landscape Appreciation, p.&nbsp;132. Upper Saddle River, NJ: Prentice Hall. .

Footnotes

  • Photo of Föhnmauer The strong clouds at the mountain ridges where the Föhn winds form are called Föhnmauer (Föhn wall).
  • Illustration
  • Movie of a Föhn situation in the Swiss Alps
  • East Scotland warmth due to Foehn Effect
  • Foehn chart provided by meteomedia/meteocentrale.ch

cs:Místní názvy větrů#Fén