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A Foehn or Föhn (, , ), is a type of dry, relatively warm, downslope wind that occurs in the lee (downwind side) 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 Orographic lift occurs when an air mass is forced from a low elevation to a higher elevation as it moves over rising terrain. As the air mass gains altitude it quickly cools down adiabatically, which can raise the relative humidity to 100% and cr ...
). 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 14 °C (25 °F) 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 The Alps () ; german: Alpen ; it, Alpi ; rm, Alps ; sl, Alpe . are the highest and most extensive mountain range system that lies entirely in Europe, stretching approximately across seven Alpine countries (from west to east): France, Sw ...
.


Etymology

The name ''Foehn'' (german: Föhn, ) arose in the
Alpine Alpine may refer to any mountainous region. It may also refer to: Places Europe * Alps, a European mountain range ** Alpine states, which overlap with the European range Australia * Alpine, New South Wales, a Northern Village * Alpine National P ...
region. Originating from Latin ''(ventus) favonius'', a mild west wind of which Favonius was the Roman personification and probably transmitted by rm, favuogn or just ''fuogn'', the term was adopted as goh, phōnno. In the Southern Alps, the phenomenon is known as ''Föhn'' but also it, favonio and ''fen'' in Serbo-Croatian and Slovene. The German word ''Föhn'' (pronounced the same way) also means "hairdryer", while the word ''Fön'' is a genericized trademark today owned by AEG. The form ''phon'' is used in French-speaking parts of Switzerland as well as in Italy. The name "Föhn" 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 The Alps () ; german: Alpen ; it, Alpi ; rm, Alps ; sl, Alpe . are the highest and most extensive mountain range system that lies entirely in Europe, stretching approximately across seven Alpine countries (from west to east): France, Sw ...
. 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" (''Alpenföhn'') was coined for the Föhns of the Alpine region.''Der Brockhaus. Wetter und Klima.'' Seite 101, Brockhaus, Leipzig/Mannheim, 2009,


Causes

There are four known causes of the Foehn warming and drying effect. These mechanisms often act together, with their contributions varying depending on the size and shape of the mountain barrier and on the meteorological conditions, such as the upstream wind speed, temperature and humidity.


Condensation and precipitation

When winds blow over elevated terrain, air forced upwards expands and cools due to the decrease in pressure with height. Since colder air can hold less water vapour, moisture condenses to form clouds and precipitates as rain or snow on the mountain's upwind slopes. The change of state from vapour to liquid water releases latent heat energy which heats the air, partially countering the cooling that occurs as the air rises. The subsequent removal of moisture as precipitation renders this heat gain by the air irreversible, leading to the warm, dry, Foehn conditions as the air descends in the mountain's lee. This mechanism has become a popular textbook example of atmospheric thermodynamics. However, the common occurrence of 'dry' Foehn events, where there is no precipitation, implies there must be other mechanisms.


Isentropic draw-down

Isentropic draw-down is the draw-down of warmer, drier air from aloft. When the approaching winds are insufficiently strong to propel the low-level air up and over the mountain barrier, the airflow is said to be 'blocked' by the mountain and only air higher up near mountain-top level is able to pass over and down the lee slopes as Foehn winds. These higher source regions provide Foehn air that becomes warmer and drier on the leeside after it is compressed with descent due to the increase in pressure towards the surface.


Mechanical mixing

When river water passes over rocks, turbulence is generated in the form of rapids, and white water reveals the turbulent mixing of the water with the air above. Similarly, as air passes over mountains, turbulence occurs and the atmosphere is mixed in the vertical. This mixing generally leads to a downward warming and upward moistening of the cross-mountain airflow, and consequently to warmer, drier Foehn winds in the valleys downwind.


Radiative warming

Dry Foehn conditions are responsible for the occurrence of rain shadows in the lee of mountains, where clear, sunny conditions prevail. This often leads to greater daytime radiative (solar) warming under Foehn conditions. This type of warming is particularly important in cold regions where snow or ice melt is a concern or where avalanches are a risk.


Effects

Winds of this type are also called "snow-eaters" for their ability to make snow and ice melt or sublimate rapidly. This is a result not only of the warmth of Foehn air, but also its low relative humidity. Accordingly, Foehn winds are known to contribute to the disintegration of ice shelves in the polar regions. Foehn winds are notorious among mountaineers in the Alps, especially those climbing the
Eiger The Eiger () is a mountain of the Bernese Alps, overlooking Grindelwald and Lauterbrunnen in the Bernese Oberland of Switzerland, just north of the main watershed and border with Valais. It is the easternmost peak of a ridge crest that extends a ...
, 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 Psychosis is a condition of the mind that results in difficulties determining what is real and what is not real. Symptoms may include delusions and hallucinations, among other features. Additional symptoms are incoherent speech and behavior t ...
. 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 The Ludwig Maximilian University of Munich (simply University of Munich or LMU; german: Ludwig-Maximilians-Universität München) is a public research university in Munich, Germany. It is Germany's sixth-oldest university in continuous operati ...
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 Codeine is an opiate and prodrug of morphine mainly used to treat pain, coughing, and diarrhea. It is also commonly used as a recreational drug. It is found naturally in the sap of the opium poppy, ''Papaver somniferum''. It is typically used ...
and the like will sometimes include ''Föhnkrankheit'' amongst the indications. Evidence for effects from
Chinook wind Chinook winds, or simply Chinooks, are two types of prevailing warm, generally westerly winds in western North America: Coastal Chinooks and interior Chinooks. The coastal Chinooks are persistent seasonal, wet, southwesterly winds blowing in from ...
s remain anecdotal. 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 theorised 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.


Local examples

Regionally, these winds are known by many different names. These include: ;in Africa *
Bergwind Berg wind (from Afrikaans ''berg'' "mountain" + ''wind'' "wind", i.e. a mountain wind) is the South African name for a katabatic wind: a hot dry wind blowing down the Great Escarpment from the high central plateau to the coast. Overview When ...
in South Africa ;in the Americas *The Brookings Effect on the southwestern coast of Oregon, also known as the Chetco Effect. *
Chinook wind Chinook winds, or simply Chinooks, are two types of prevailing warm, generally westerly winds in western North America: Coastal Chinooks and interior Chinooks. The coastal Chinooks are persistent seasonal, wet, southwesterly winds blowing in from ...
s east of the
Rocky Mountains The Rocky Mountains, also known as the Rockies, are a major mountain range and the largest mountain system in North America. The Rocky Mountains stretch in straight-line distance from the northernmost part of western Canada, to New Mexico in ...
and the
Cascade Range The Cascade Range or Cascades is a major mountain range of western North America, extending from southern British Columbia through Washington and Oregon to Northern California. It includes both non-volcanic mountains, such as the North Cascades, ...
in the United States and Canada, and north, east and west of the
Chugach Mountains The Chugach Mountains of southern Alaska are the northernmost of the several mountain ranges that make up the Pacific Coast Ranges of the western edge of North America. The range is about long and wide, and extends from the Knik and Turnaga ...
of Alaska, United States * Foehn winds in the foothills of the southern Appalachian mountains, 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 *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 A katabatic wind (named from the Greek word κατάβασις ''katabasis'', meaning "descending") 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 sometim ...
. * Puelche wind in Chile *
Suêtes Suetes, ''suêtes'', ''les suêtes'', are strong south-east foehn winds on the west coast of Cape Breton Island. The term "suête" originates from the Acadian French inhabitants of the Chéticamp area as a contraction of "sud est" (south-east). ...
on the west coast of
Cape Breton Island Cape Breton Island (french: link=no, île du Cap-Breton, formerly '; gd, Ceap Breatainn or '; mic, Unamaꞌki) is an island on the Atlantic coast of North America and part of the province of Nova Scotia, Canada. The island accounts for 18. ...
, Nova Scotia, Canada *
Zonda wind Zonda wind ( es, viento zonda) is a regional term for the foehn wind that often occurs on the eastern slope of the Andes, in Argentina. Formation The Zonda is a dry wind (often carrying dust) which comes from the polar maritime air, warmed by de ...
s in
Argentina Argentina (), officially the Argentine Republic ( es, link=no, República Argentina), is a country in the southern half of South America. Argentina covers an area of , making it the second-largest country in South America after Brazil, th ...
;in Antarctica * Föhn wall on
Signy Island Signy Island is a small subantarctic island in the South Orkney Islands of Antarctica. It was named by the Norwegian whaler Petter Sørlle (1884–1933) after his wife, Signy Therese. The island is about long and wide and rises to above s ...
,
South Orkneys The South Orkney Islands are a group of islands in the Southern Ocean, about north-east of the tip of the Antarctic PeninsulaGilan region (near the
Alborz The Alborz ( fa, البرز) range, also spelled as Alburz, Elburz or Elborz, is a mountain range in northern Iran that stretches from the border of Azerbaijan along the western and entire southern coast of the Caspian Sea and finally runs nort ...
) in the south west of
Caspian Sea The Caspian Sea is the world's largest inland body of water, often described as the world's largest lake or a full-fledged sea. An endorheic basin, it lies between Europe and Asia; east of the Caucasus, west of the broad steppe of Central Asi ...
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 Region and Hakkâri Province in Turkey). For example, the winter rainfall of Urmia and Salmas in Iranian Azerbaijan is much lower than
Batifa Batifa ( ar, باطوفا, ku, باتيفا, Batîfa) is a town and sub-district in Dohuk Governorate in Kurdistan Region, Iraq. It is located in the Zakho District. Villages Geography Climate Batufa has a hot-summer Mediterranean climate ('' ...
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 The Zagros Mountains ( ar, جبال زاغروس, translit=Jibal Zaghrus; fa, کوه‌های زاگرس, Kuh hā-ye Zāgros; ku, چیاکانی زاگرۆس, translit=Çiyakani Zagros; Turkish: ''Zagros Dağları''; Luri: ''Kuh hā-ye Zāgr ...
. * Loo in
Indo-Gangetic Plain The Indo-Gangetic Plain, also known as the North Indian River Plain, is a fertile plain encompassing northern regions of the Indian subcontinent, including most of northern and eastern India, around half of Pakistan, virtually all of Bangla ...
*
Warm Braw Warm Braw is a foehn wind in the Schouten Islands north of New Guinea New Guinea (; Hiri Motu: ''Niu Gini''; id, Papua, or , historically ) is the world's second-largest island with an area of . Located in Oceania in the southwestern Pa ...
in the
Schouten Islands The Schouten Islands ( id, Kepulauan Biak, also Biak Islands or Geelvink Islands) are an island group of Papua province, eastern Indonesia in the Cenderawasih Bay (or Geelvink Bay) 50 km off the north-western coast of the island of New ...
north of West Papua, Indonesia. *
Wuhan Wuhan (, ; ; ) is the capital of Hubei Province in the People's Republic of China. It is the largest city in Hubei and the most populous city in Central China, with a population of over eleven million, the ninth-most populous Chinese city an ...
in China is famously known as one of the
Three Furnaces The term Three Furnaces () refers to the especially hot and oppressively humid summer weather in several major cities in the Yangtze River Valley, within China. It was coined during the ROC period of China, and refers to the following cities: * ...
on account of its extremely hot weather in summer resulting from the adiabatic warming effect created by mountains further south. *Laos wind ( vi, gió Lào), hot-dry west wind ( vi, gió tây khô nóng) in northern and central Vietnam. ;in Europe * Favonio in
Ticino Ticino (), sometimes Tessin (), officially the Republic and Canton of Ticino or less formally the Canton of Ticino,, informally ''Canton Ticino'' ; lmo, Canton Tesin ; german: Kanton Tessin ; french: Canton du Tessin ; rm, Chantun dal Tessin . ...
and north-western Italy due to western and northern winds crossing the
Alps The Alps () ; german: Alpen ; it, Alpi ; rm, Alps ; sl, Alpe . are the highest and most extensive mountain range system that lies entirely in Europe, stretching approximately across seven Alpine countries (from west to east): France, Sw ...
(mostly in winter) *Garbino in the
Adriatic The Adriatic Sea () is a body of water separating the Italian Peninsula from the Balkan Peninsula. The Adriatic is the northernmost arm of the Mediterranean Sea, extending from the Strait of Otranto (where it connects to the Ionian Sea) to the ...
coast of Italy due to south-western winds crossing the
Apennine Mountains The Apennines or Apennine Mountains (; grc-gre, links=no, Ἀπέννινα ὄρη or Ἀπέννινον ὄρος; la, Appenninus or  – a singular with plural meaning;''Apenninus'' (Greek or ) has the form of an adjective, which wou ...
(mostly in fall and winter) * Fen in northwest Slovenia * Fønvind in
South Norway South Norway (, ) is the southern and by far most populous half of Norway, consisting of the regions of Western Norway, Eastern Norway, Southern Norway (Agder) and Trøndelag (Central Norway). In English, South Norway was historically also known ...
, in particular
Central Norway Central Norway ( nb, Midt-Norge, nn, Midt-Noreg) is an informal region of Norway that is not clearly defined. The term ''Central Norway'' may in its most limited usage refer only to Trøndelag county, but may also be understood to include all or ...
, resulting in extreme winter warming, including Scandinavia's warmest winter temperature in
Sunndalsøra is the administrative centre of Sunndal Municipality in Møre og Romsdal county, Norway. The village of Sunndalsøra lies at the mouth of the river Driva at the beginning of the Sunndalsfjord. Sunndalsøra is surrounded by steep mountains, suc ...
. * Fogony in the
Catalan Catalan may refer to: Catalonia From, or related to Catalonia: * Catalan language, a Romance language * Catalans, an ethnic group formed by the people from, or with origins in, Northern or southern Catalonia Places * 13178 Catalan, asteroid #1 ...
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 Halny is a foehn wind that blows in southern Poland and in Slovakia in the Tatra Mountains of the Carpathians. The most turbulent halny blows in Podhale region of southern Poland, coming from the south, down the slopes of the Tatra Mountains; in Sl ...
in the Carpathian Mountains, Poland (Central Europe) *The
Helm Wind The Helm Wind is a named wind in Cumbria, England, a strong north-easterly wind which blows down the south-west slope of the Cross Fell escarpment. It is the only named wind in the British Isles, although many other mountain regions in Britain ...
, on the Pennines in the Eden Valley, Cumbria, England *Hnjúkaþeyr in Icelandic * Livas wind in the
Thessalian plain The Thessalian plain ( el, Θεσσαλική πεδιάδα, Θεσσαλικός κάμπος) is the dominant geographical feature of the Greek region of Thessaly. The plain is formed by the Pineios River and its tributaries and is surrounded ...
,
Boeotia Boeotia ( ), sometimes Latinized as Boiotia or Beotia ( el, Βοιωτία; modern: ; ancient: ), formerly known as Cadmeis, is one of the regional units of Greece. It is part of the region of Central Greece. Its capital is Livadeia, and it ...
plain, Plain of Thessaloniki, Elefsina and Athens in Greece * Košava (Koshava) wind in Serbia that blows along the Danube River *Nortada in
Cascais Cascais () is a town and municipality in the Lisbon District of Portugal, located on the Portuguese Riviera. The municipality has a total of 214,158 inhabitants in an area of 97.40 km2. Cascais is an important tourist destination. Its marina ...
, and most notoriously in
Guincho Beach Praia do Guincho (English: Guincho Beach) is an Atlantic beach located on Portugal's Estoril coast, 5 km from the town of Cascais, and is located in the municipality of Cascais, more precisely in the parishes of Cascais and Alcabideche, in t ...
, making it one of the best windsurfing spots in Europe *Ponentà in Valencia (eastern Spain) *Terral in
Málaga Málaga (, ) is a Municipalities of Spain, municipality of Spain, capital of the Province of Málaga, in the Autonomous communities of Spain, autonomous community of Andalusia. With a population of 578,460 in 2020, it is the second-most populou ...
(southern Spain) * Vântul Mare in the Carpathian Mountains, Romania *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 The Great Dividing Range, also known as the East Australian Cordillera or the Eastern Highlands, is a cordillera system in eastern Australia consisting of an expansive collection of mountain ranges, plateaus and rolling hills, that runs roug ...
, observed in the coastal plains of New South Wales, and also in eastern
Victoria Victoria most commonly refers to: * Victoria (Australia), a state of the Commonwealth of Australia * Victoria, British Columbia, provincial capital of British Columbia, Canada * Victoria (mythology), Roman goddess of Victory * Victoria, Seyche ...
and eastern Tasmania. *The Nor'wester in
Hawkes Bay Hawke's Bay ( mi, Te Matau-a-Māui) is a local government region on the east coast of New Zealand's North Island. The region's name derives from Hawke Bay, which was named by Captain James Cook in honour of Admiral Edward Hawke. The region ...
,
Canterbury Canterbury (, ) is a cathedral city and UNESCO World Heritage Site, situated in the heart of the City of Canterbury local government district of Kent, England. It lies on the River Stour. The Archbishop of Canterbury is the primate of the ...
, and
Otago Otago (, ; mi, Ōtākou ) is a region of New Zealand located in the southern half of the South Island administered by the Otago Regional Council. It has an area of approximately , making it the country's second largest local government reg ...
, New Zealand


In popular culture

* The Foehn was mentioned by Queen's lead guitarist Brian May while talking about the band's grim Munich recording studio experience in 1982. * The foehn is attributed by the narrator of
Jens Bjørneboe Jens Ingvald Bjørneboe (9 October 1920 – 9 May 1976) was a Norwegian writer whose work spanned a number of literary formats. He was also a painter and a Waldorf school teacher. Bjørneboe was a harsh and eloquent critic of Norwegian society an ...
's 1966 novel ''Frihetens øyeblikk'' (''Moment of Freedom'') as the traditional cause of occasional unprovoked murders in a small Alpine town. * "Foehn" is the last word in ''A Nest of Ninnies'', a 1969 novel by John Ashbery and
James Schuyler James Marcus Schuyler (November 9, 1923 – April 12, 1991) was an American poet. His awards include the Pulitzer Prize for Poetry for his 1980 collection ''The Morning of the Poem''. He was a central figure in the New York School (art), New ...
. Ashbery claimed that he and Schuyler chose this particular word because "people, if they bothered to, would have to open the dictionary to find out what the last word in the novel meant." * Fønfjord, meaning "Foehn Fjord," was named by Arctic explorer
Carl Ryder 200px, Schooner '' Fylla'' in Copenhagen harbour Carl Hartvig Ryder (12 September 1858 – 3 May 1923) was a Danish naval officer and Arctic explorer. Biography Carl Ryder was born in Copenhagen. He was the son of Frederik Valentiner Ryder (182 ...
after the powerful Foehn wind gusts blowing during the first exploration of the fjord in August 1891.


Gallery

File:Pájara Morro Jable - Carretera Punta de Jandía - cemetery + foehn 01 ies.jpg, Foehn over Carretera Punta de Jandía in
Morro Jable Morro Jable is a locality belonging of the municipality of Pájara, in the island of Fuerteventura, Canary Islands, Spain. With around 7,000 inhabitants as of 2020, it is the most populated settlement in the municipality. It was founded by Cirilo ...
,
Pájara Pájara is a municipality in the southwestern portion of the island of Fuerteventura in the Province of Las Palmas in the Canary Islands as well as the name of its largest town. Its population is 20,931 (2013),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 The Alps () ; german: Alpen ; it, Alpi ; rm, Alps ; sl, Alpe . are the highest and most extensive mountain range system that lies entirely in Europe, stretching approximately across seven Alpine countries (from west to east): France, Sw ...
.


See also

*
Alpine climate Alpine climate is the typical weather (climate) for elevations above the tree line, where trees fail to grow due to cold. This climate is also referred to as a mountain climate or highland climate. Definition There are multiple definitions of ...
*
Anabatic wind An anabatic wind, from the Greek '' anabatos'', verbal of ''anabainein'' meaning moving upward, is a warm wind which blows up a steep slope or mountain side, driven by heating of the slope through insolation.Föhn cloud *
Katabatic wind A katabatic wind (named from the Greek word κατάβασις ''katabasis'', meaning "descending") 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 sometim ...
s * Lee wave *
Meteorology Meteorology is a branch of the atmospheric sciences (which include atmospheric chemistry and physics) with a major focus on weather forecasting. The study of meteorology dates back millennia, though significant progress in meteorology did not ...


References

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


Footnotes


External links


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


{{Authority control Föhn effect Mountain meteorology Weather and health Wind Winds cs:Místní názvy větrů#Fén