A fÃÆ'¶hn or foehn ( UK: , US: ) is a dry, warm, down-slope type that occurs in the lee (windward side) of the mountains.
This is a rain of wind shadows resulting from subsequent adiabatic air heating that has dropped most of its moisture on the wind slopes (see orographic lift). As a result of different adiabatic hose levels of moist and dry air, the air on the lower slopes becomes warmer than the equivalent altitude on the wind slopes. Wind FÃÆ'¶hn can raise temperatures by 14 Â ° C (25 Â ° F) in just minutes. Central Europe enjoys a warmer climate due to FÃÆ'¶hn, as the damp breezes of the Mediterranean Sea blow over the Alps.
In some areas, wind fÃÆ'¶hn is associated with causing "circulatory problems", headaches, or similar illnesses. Researchers have found, however, that warm temperatures of foehn winds are beneficial to humans in most situations, and have theorized that the reported negative effects may be the result of secondary factors, such as changes in electric fields or in ionic status from the atmosphere, relatively low, or generally unpleasant sensations in an environment with strong winds and strong winds.
Video Foehn wind
Cause
The explanation of warming and the effects of drying in popular literature or on the web is often a causal mechanism (# 1 - Condensation and Precipitation - below), but there are actually four known causes (illustrated in the scheme above the right of this page). These mechanisms often act together, with their contribution varying depending on the size and shape of the mountain barrier and on meteorological conditions, such as wind speed, temperature and upstream humidity.
1) Condensation and precipitation : As air is pushed upwards above the plateau, it expands and cools due to the drop in pressure with altitude. Because the cooler air can hold less water vapor, the dew condenses into clouds and settles as rain or snow on the mountainside against the wind. The change of state from steam to liquid water is accompanied by heating, and subsequent moisture removal as rain makes this heat irreversible, leading to a dry and warm foehn condition on the mountain. This mechanism has become a popular book example of atmospheric thermodynamics and it is suitable for interesting diagrams. But the common occurrence of the 'dry' fungus event, where there is no rain, implies there must be other mechanisms.
2) Isentropic draw-down (warmer withdrawal, drier air from above): When the approaching wind is not strong enough to push the low-level air up and over the mountain barrier , the airflow is said to be 'blocked' by the mountain and only the higher air near the level of a mountain peak that is able to pass through and descend the slopes as high winds. These higher source areas provide warmer and drier frozen air at the seaside after being compressed with decreases due to increased surface pressure.
3) Mechanical mixing : When the river water passes through the rocks, turbulence is generated in the form of rapids, and the white water reveals the turbulent mixing of water with the air above. Similarly, when air passes through a mountain, turbulence occurs and the atmosphere mixes in the vertical. This mixing generally leads to a downward and upward warming that moisturizes mountain airflow, and consequently warmer, drier winds in the valleys are in the direction of the wind.
4) Radiant heating : Dry conditions are responsible for the occurrence of rain shadows in mountainous lees, where bright and sunny conditions prevail. This often leads to heating of greater solar radiation (sun) under weather conditions. This type of heating is very important in cold areas where snow or ice is melting is a concern and/or avalanches are risks.
Maps Foehn wind
Effects
This type of wind is also called "snow-eaters" because of their ability to make snow and ice melt or sublimate quickly. This is not only the result of warm air, but also its low relative humidity. Thus, foehn winds are known to contribute to the disintegration of the ice sheets in the polar regions.
Foehn winds are famous among mountain climbers in the Alps, especially those who climb the Eiger, where the winds add further difficulty in climbing the already difficult peak.
They are also linked to the rapid spread of forest fires, leaving some of these wind-proof areas particularly vulnerable to fires.
Anecdotally, residents in the wind region often report foehn various diseases ranging from migraines to psychosis. The first clinical review of this effect was published by Austrian physician Anton Czermak in the 19th century. A study by Ludwig-Maximilians-UniversitÃÆ'¤t MÃÆ'¼nchen found that suicide and accidents increased 10 percent during the wind blowing in Central Europe. The cause of FÃÆ'¶hnkrankheit (English: Foehn-sickness) has not been proven. Labeling for the preparation of aspirin combined with caffeine, codeine and the like will sometimes include FÃÆ'¶hnkrankheit among the indications. The evidence for the effects of the Chinook wind remains anecdotal.
Etymology
Name Foehn (German: FÃÆ'¶hn , pronounced ['fÃÆ'¸: n] ) appears in the Alpine region. Derived from the Latin (ventus) favonius , a gentle western wind where Favonius is Roman personification and may be transmitted by Romansh: favuogn > or just fuogn , this term is adopted as Old High German: ph? nno . In Southern Alps, this phenomenon is known as fÃÆ'¶hn but also Italian: favonio and fen in Croatian and Slovenian. The German word "FÃÆ'¶n" (without "H", but pronounced in the same way), generic trademark, also means "hair dryer," and phon form is used in the French-speaking part of Switzerland as well as in Italy. The form of "fen" is used in Croatia and Slovenia.
Local example
Source of the article : Wikipedia
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