A foehn wind or föhn wind is a type of dry downslope wind which occurs in the lee of a mountain range. It is a rain shadow wind which results from the subsequent adiabatic warming of air which has dropped most of its moisture on windward slopes (seeorographic 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. Föhn winds can raise temperatures by as much as 30°C (54°F) in just a matter of hours. Central Europe enjoys a warmer climate due to the Föhn.
Winds of this type are called "snow-eaters" for their ability to make snowmelt (also sublimate) rapidly. This snow-removing ability is caused not only by warmer temperatures, but also the low relative humidity of the air mass, having been stripped of moisture by orographic precipitation coming over the mountain(s).
Föhn winds are notorious among mountaineers in the Alps, especially those climbing the Eiger, for whom the winds add additional 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.
These winds are often associated with illness ranging from migraines to psychosis. A study by the Ludwig-Maximilians-Universität München found that suicide and accidents increased by 10 percent during föhn winds in Central Europe. The causation of Föhnkrankheit (English: Föhn-sickness) is yet unproven. Labelling for preparations of aspirin combined with caffeine, codeine and the like will sometimes include Föhnkrankheit amongst the indications.
Etymology
The name föhn (from the GermanFöhn, pronounced [føːn]) originated in the alpine region. From Latin (ventus) favonius, a mild west wind of which Favonius was the Roman personification.[1]
Local examples
Regionally, these winds are known by many different names. These include:
The threat of the Föhn drives the protaganists Ayla and Jondalar in Jean M. Auel's The Plains Of Passage over a glacier before the spring melt. The pair make refereces to the mood altering phenomena of the wind, similar to those of the Santa Ana wind.
Fön trademark
AEG registered the trademark Fön in the 1920s for its hairdryer, which is widely used as a synonym in several languages, such as German, Swiss German, Danish, Italian, Dutch, Norwegian, Czech, Croatian, Latvian, Romanian, Slovak, Slovenian, Swedish, Turkish and French in western Switzerland.
McKnight, TL & Hess, Darrel (2000). Foehn/Chinoonk Winds. In , Physical Geography: A Landscape Appreciation, pp. 132. Upper Saddle River, NJ: Prentice Hall. ISBN 0130202630
Footnotes
^Concise Oxford Dictionary, 10th edition, Oxford University Press, entry föhn.