{{Short description|Type of dry down-slope wind occurring the lee of mountain ranges}} {{Redirect|Föhn|the antiaircraft rocket|Henschel Hs 297}} {{Use American English|date=November 2024}} [[File:Foehn effect mechanisms.png|thumb|270px|The causes of the Foehn effect in the lee of mountains (adapted from:<ref name="The Causes of Foehn Warming in the">{{cite journal|last1=Elvidge|first1=Andrew D.|last2=Renfrew|first2=Ian A.|title=The Causes of Foehn Warming in the Lee of Mountains|journal=Bulletin of the American Meteorological Society|date=14 May 2015|volume=97|issue=3|pages=455–466|doi=10.1175/bams-d-14-00194.1|ref=4|bibcode=2016BAMS...97..455E|doi-access=free}}</ref>)]] [[File:Cumbre Nueva 2014-05.JPG|thumb|260px|Dissolving [[Föhn cloud]]s over [[Cumbre Nueva]], [[La Palma]], at an elevation of {{cvt|1,400|m|ft}}]]
A '''Foehn''', or '''Föhn''' ({{IPA|DE|føːn}}; {{IPAc-en|UK|f|ɜː|n}}, {{IPAc-en|US|f|eɪ|n}} {{respell|fayn}},<ref>{{cite EPD|18}}</ref><ref>{{cite LPD|3}}</ref> {{IPAc-en|usalso|f|ʌ|n|,_|f|ɜːr|n}} {{respell|fu(r)n}}<ref>{{cite DPCE|2}}</ref><ref>{{cite Merriam-Webster|foehn|access-date=2022-03-17}}</ref>), is a type of dry, relatively warm [[katabatic wind|downslope wind]] in the [[leeward|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 and leeward|windward]] slopes (see [[orographic lift]]). As a consequence of the different adiabatic [[lapse rate]]s of moist and dry air, the air on the leeward slopes becomes warmer than equivalent [[elevation]]s on the windward slopes.
Foehn winds can raise [[atmospheric temperature|temperatures]] by as much as {{cvt|14|C-change}}<ref name="NOAA-SD">{{cite web |title=South Dakota Weather History and Trivia for January |url=https://crh.noaa.gov/fsd/?n=fsdtrivia01 |publisher=[[National Weather Service]] [[list of National Weather Service Weather forecast offices|Weather Forecast Office]] |date=February 8, 2006 |at=See January 22 entry |access-date=July 15, 2024 |archive-date=December 19, 2014 |archive-url=https://web.archive.org/web/20141219030748/http://www.crh.noaa.gov/fsd/?n=fsdtrivia01 |url-status=dead }}</ref> 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'' ({{langx|de|Föhn}}, {{IPA|de|ˈføːn|pron}}) arose in the [[Alps|Alpine]] region. Originating from Latin {{lang|la|(ventus) favonius}}, a mild west wind of which [[Zephyrus|Favonius]] was the Roman personification<ref>''Concise Oxford Dictionary'', 10th edition, Oxford University Press, entry ''föhn''.</ref> and probably transmitted by {{langx|rm|favuogn}} or just {{lang|rm|fuogn}}, the term was adopted as {{langx|goh|phōnno}}. In the Southern Alps, the phenomenon is known as {{lang|de|Föhn}} but also {{langx|it|favonio}} and {{lang|sh|fen}} in [[Serbo-Croatian language|Serbo-Croatian]] and [[Slovene language|Slovene]]. The German word {{lang|de|Föhn}} (pronounced the same way) also means 'hairdryer', while the word {{lang|de|Fön}} is a [[genericized trademark]] today owned by [[AEG (German company)|AEG]].<ref>{{cite web|title=22. Januar 2009 – Vor 100 Jahren: "Fön" ins Markenregister eingetragen|periodical=WDR.de|url=https://www1.wdr.de/stichtag/stichtag4002.html|access-date=2019-12-21|date=2009-01-22}}</ref> The form ''phon'' is used in [[Romandy|French-speaking parts of Switzerland]] as well as in [[Northern Italy|Northern Italy.]]
The name {{lang|de|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]]. 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]]" ({{lang|de|Alpenföhn}}) was coined for the Föhns of the Alpine region.<ref name="Brockhaus">''Der Brockhaus. Wetter und Klima.'' Seite 101, Brockhaus, Leipzig/Mannheim, 2009, {{ISBN|978-3-7653-3381-1}}</ref>
== Causes == [[File:Val cenis stausee.jpg|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.<ref name="The Causes of Foehn Warming in the"/> 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 vapor, moisture condenses to form clouds and precipitates as rain or snow on the mountain's upwind slopes. The change of state from vapor 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.
[[File:Foehn rotor cloud.jpg|thumb|Rotor cloud revealing overturning and turbulence above the lee slopes of the Antarctic Peninsula during a westerly Foehn event]]
===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 == {{more citations needed section|date=February 2013}} Winds of this type are also called "snow-eaters" for their ability to make snow and ice melt or [[Sublimation (chemistry)|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.<ref>{{cite journal|last1=Elvidge|first1=Andrew D.|last2=Renfrew|first2=Ian A.|last3=King|first3=John C.|last4=Orr|first4=Andrew|last5=Lachlan-Cope|first5=Tom A.|title=Foehn warming distributions in nonlinear and linear flow regimes: a focus on the Antarctic Peninsula|journal=Quarterly Journal of the Royal Meteorological Society|date=January 2016|volume=142|issue=695|pages=618–631|doi=10.1002/qj.2489|ref=11|bibcode=2016QJRMS.142..618E|url=http://nora.nerc.ac.uk/id/eprint/508840/1/qj2489.pdf|doi-access=free}}</ref>
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 [[wildfire]]s, 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 [[migraine]]s to [[psychosis]]. The first clinical review of these effects was published by the Austrian physician Anton Czermak in the 19th century.<ref>{{cite journal | last1 = Giannini | first1 = AJ | last2 = Malone | first2 = DA | last3 = Piotrowski | first3 = TA | title = The serotonin irritation syndrome – a new clinical entity? | journal = The Journal of Clinical Psychiatry | volume = 47 | issue = 1 | pages = 22–25 | year = 1986 | pmid = 2416736 }}</ref> A study by the [[Ludwig-Maximilians-Universität München]] found that [[suicide]] and accidents increased by 10 percent during Foehn winds in Central Europe.{{citation needed|date=May 2009}} 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.{{Citation needed|date=February 2013}}<ref>See the documentary: Snow Eater (the English translation of Canadian First Nations word phonetically pronounced chinook). [http://www.telefilm.ca/en/catalogues/production/snow-eater telefilm.ca] {{webarchive|url=https://web.archive.org/web/20131017040732/http://www.telefilm.ca/en/catalogues/production/snow-eater |date=2013-10-17 }}.</ref> Evidence for effects from [[Chinook wind]]s remains anecdotal, as it does for New Zealand's [[Nor'west arch|Nor'wester]].<ref>Brook, K., "[https://www.canterbury.ac.nz/news/2014/grumpy-norwest-winds-.html Grumpy nor'west winds]," [[University of Canterbury]], 2 December 2014. Retrieved 22 November 2023.</ref>
In some regions, Foehn winds are associated with causing circulatory problems, headaches, or similar ailments.<ref name="tuller">{{cite journal|last1=Tuller|first1=Stanton E.|title=The Effects of a Foehn Wind on Human Thermal Exchange: The Canterbury Nor'wester|journal=New Zealand Geographer|date=April 1980|volume=36|issue=1|pages=11–19|doi=10.1111/j.1745-7939.1980.tb01919.x|bibcode=1980NZGeo..36...11T }}</ref> 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.<ref name="tuller"/>
== Local examples == {{more citations needed section|date=February 2018}} Regionally, these winds are known by many different names. These include:
;in the Americas *The [[Brookings effect|Brookings Effect]] on the southwestern coast of Oregon, also known as the Chetco Effect. * [[Chinook wind]]s east of the [[Rocky Mountains]] and the [[Cascade Range]] in the United States and Canada, and north, east and west of the [[Chugach Mountains]] of Alaska, United States * Foehn winds in the foothills of the southern [[Appalachian Mountains]],<ref>{{cite journal|author=David M. Gaffin|title=Foehn Winds That Produced Large Temperature Differences near the Southern Appalachian Mountains|journal=Weather and Forecasting|date=2007|volume=22|issue=1|pages=145–159|url=https://journals.ametsoc.org/waf/article/22/1/145/38793/Foehn-Winds-That-Produced-Large-Temperature|bibcode=2007WtFor..22..145G|doi=10.1175/WAF970.1|citeseerx=10.1.1.549.7012|s2cid=120049170 }}</ref> 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<ref>{{cite journal|author=David M. Gaffin|title=Unexpected Warming Induced by Foehn Winds in the Lee of the Smoky Mountains|journal=Weather and Forecasting|date=2002|volume=17|issue=4|pages=907–915|bibcode=2002WtFor..17..907G|doi=10.1175/1520-0434(2002)017<0907:UWIBFW>2.0.CO;2|doi-access=free}}</ref> *[[Mono winds]] in the [[Sierra Nevada]].<ref>{{cite journal | last1=Ruscha | first1=Charles P. Jr. |date=February 1976 |title=Forecasting the Mono Wind |url=https://www.weather.gov/media/wrh/online_publications/TMs/TM-105.pdf |journal=National Oceanic and Atmospheric Administration |volume=NWS WR-105 |issue= |pages= |doi= |access-date=November 22, 2021}}</ref> *The [[Santa Ana winds]] of southern [[California]], including the [[Sundowner (wind)|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 Mountains|Santa Monica]] and [[Santa Ana Mountains|Santa Ana]] Mountains and their respective leeward valleys, the [[San Fernando Valley]] and the [[Riverside County, California|Riverside County]] portion of the [[Inland Empire (California)|Inland Empire]] region. *[[Puelche (wind)|Puelche wind]] in Chile *[[Suêtes]] on the west coast of [[Cape Breton Island]], [[Nova Scotia]], Canada *[[Wreckhouse, Newfoundland and Labrador|Wreckhouse]] winds in the southwest corner of the island of [[Newfoundland]], [[Newfoundland and Labrador]], Canada *[[Zonda wind]]s in Argentina
;in Antarctica * Föhn wall on [[Signy Island]], [[South Orkneys]]
;in Asia * Garmesh, Garmij, Garmbaad ({{Translation|Warm wind|literal=yes}}): ({{langx|fa|گرمباد}}, {{langx|glk|گرمش}}) 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|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, Iraq|Soran]] in Iraqi Kurdistan, and [[Hakkâri (city)|Hakkâri]] in the Hakkâri Province, which are roughly on the same latitude but are on the windward side of the [[Zagros Mountains]]. * [[Loo (wind)|Loo]] in [[Indo-Gangetic Plain]] *[[Warm Braw]] in the [[Schouten Islands]] north of [[West Papua (province)|West Papua]], Indonesia.<ref>{{cite web|url=http://ggweather.com/winds.html|title=Wind Names|work=ggweather.com}}</ref> *[[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 ({{langx|vi|gió Lào}}), hot-dry west wind ({{langx|vi|gió tây khô nóng}}) in northern and central Vietnam.
;in Europe [[File:Mittagskogel Foehnwolken 15032008 01.jpg|thumb|Foehn clouds upon the [[Karawanken]] mountain range, [[Carinthia]], Austria]] [[File:Cascada de nubes La Palma 20080606.jpg|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 Sea|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 [[Catalonia|Catalan]] [[Pyrenees]] * Föhn or Foehn in Austria, southern Germany, Switzerland, France and Liechtenstein *Föhn in [[Ostrobothnia (administrative region)|Ostrobothnia]] and Western [[Lapland (Finland)|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 [[River Eden, Cumbria|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 (wind)|Košava]] (Koshava) wind in Serbia that blows along the river [[Danube]]<ref>{{cite journal|last1=Romanić|title=Contributing factors to Koshava wind characteristics|journal=International Journal of Climatology|volume=36|issue=2|pages=956–973|date=2015|doi=10.1002/joc.4397|display-authors=etal|bibcode = 2016IJCli..36..956R |s2cid=129669216 }}</ref><ref>{{cite journal|last1=Romanić|title=Long-term trends of the 'Koshava' wind during the period 1949–2010|journal=International Journal of Climatology|date=2015|volume=35|issue=3|pages=288–302|doi=10.1002/joc.3981|display-authors=etal|bibcode = 2015IJCli..35..288R |s2cid=129402302 }}</ref> *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 [[Green Spain|Cantabrian region]] (northern Spain)
;in Oceania *The [[Australian foehn winds|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 (state)|Victoria]] and eastern [[Tasmania]].<ref>Sharples, J.J. Mills, G.A., McRae, R.H.D., Weber, R.O. (2010) ''Elevated fire danger conditions associated with foehn-like winds in southeastern Australia. Journal of Applied Meteorology and Climatology''.</ref> *The [[Nor'west arch|Nor'wester]] in [[Hawkes Bay]], [[Canterbury, New Zealand|Canterbury]], and [[Otago]], New Zealand<ref>Relph, D. "[https://www.nzgeo.com/stories/the-canterbury-norwester/ The Canterbury nor'wester]," ''New Zealand Geographic''. Retrieved 17 February 2018.</ref>
==Gallery== <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 wind]]s * [[Lee wave]] * [[Meteorology]]
== References == * McKnight, TL & Hess, Darrel (2000). "Foehn/Chinook Winds". In ''Physical Geography: A Landscape Appreciation'', p. 132. Upper Saddle River, NJ: Prentice Hall. {{ISBN|0-13-020263-0}}.
=== Footnotes === {{Reflist}}
== External links == {{commons}} {{EB1911 poster|Föhn}} * [http://www.wolkenatlas.de/wolken/wo12234.htm Photo of Föhnmauer] The strong clouds at the mountain ridges where the Föhn winds form are called ''Föhnmauer'' (Föhn wall). * [http://www.bom.gov.au/lam/glossary/fpagegl.shtml#fo Illustration] * [https://www.flickr.com/photos/snowfactory/2756402718/ Movie of a Föhn situation in the Swiss Alps] * [https://web.archive.org/web/20120322125424/http://www.bbc.co.uk/weather/feeds/17448378 East Scotland warmth due to Foehn Effect] * [http://www.meteocentrale.ch/de/wetter/foehn-und-bise/foehn.html Foehn chart provided by meteomedia/meteocentrale.ch] {{Webarchive|url=https://web.archive.org/web/20130403060503/http://www.meteocentrale.ch/de/wetter/foehn-und-bise/foehn.html |date=2013-04-03 }}
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[[Category:Föhn effect]] [[Category:Mountain meteorology]] [[Category:Weather and health]] [[Category:Wind]] [[Category:Winds]]
[[cs:Místní názvy větrů#Fén]]