A foehn wind or föhn wind is a type of dry down slope 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 (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. 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.
Contents |
Winds of this type are called "snow-eaters" for their ability to make snow melt (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.
The name föhn (from the German Föhn, pronounced [ˈføːn]) originated in the alpine region. From Latin (ventus) favonius, a mild west wind of which Favonius was the Roman personification.[1]
Regionally, these winds are known by many different names. These include:
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.