school energy&environment

The Foehn wind

The name Föhn (or Foehn) comes from the dialect of Tyrol, and indicates a particular type of wind that is characteristic in the Alps, which can also be noted, naturally, in most of the other mountain ranges. It is generated when a moving mass of warm humid air meets a mountain on its path. By inertia, the mass of air moves against the mountain and the air is forced to rise along the sides of the mountain. As it rises, the air cools and expands, thus becoming saturated with water vapour. Clouds are formed and the excess humidity is released in the form of abundant liquid precipitations or snowfall. Because of the heat that is freed during the condensation, the air that rises to the peak of the mountain is at a higher temperature than what it would have been had it been dry.
When it passes the mountain crest, after having discharged most of its humidity, the air that is now dry, blows across the opposite side of the mountain and becomes warmer as it descends. In the Alps, masses of air rise along the northern slopes (Switzerland and Austria) , with the formation of clouds and precipitation, and the warm air descends on the Italian slopes, where the weather conditions become fair, with clear blue skies and temperatures that are 10-20° C higher than on the Northern slopes. This phenomenon guarantees winter days that are mild and very clear in Northern Italy, with strong winds that blow away the fog and pollution that hover above the big cities due to inversion, while on the other side of the mountains, the weather conditions are bad.
This phenomenon explains why snowfall is generally more plentiful on the northern slopes of the mountain range. This type of atmospheric phenomenon is very dangerous in case of heavy snowfall, because since it favours high temperature conditions, it also brings about the melting of the layer of snow and increases the risk of avalanches. Therefore, skiers must pay attention on clear winter days that are unexpectedly warm. And if you leave Milan on a wonderful clear morning, to ski on the Swiss snow, be careful. If the mountain crests at the frontier are capped with thin feathery clouds, swept by the wind, you may find bad weather conditions awaiting you on the other side!
However, the Foehn’s misdeeds are not limited to this; when the warm dry air that travels at a high speed is blown over the mountains, the wind has the capacity to charge the air with electricity, increasing the number of positive ions. Our body reacts negatively to positive electric charges, and in “meteoropathic” subjects who are particularly sensitive to the variations in the weather, this provokes nervousness, anxiety, migraine and irritability. A statistical study carried out in Switzerland, where this wind is called Favonio, correlated the days of Foehn winds with an increase in the number of suicides, homicides and aggressions.