Mistral (wind)
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The Mistral in France is a fresh or cold, often violent, and usually dry wind, blowing throughout the year but is most frequent in winter and spring. It blows from the northwest or north of Europe through the valley of the Rhône River to the Mediterranean.[1] It also affects the whole of Sardinia in Italy.
In the south of France the name comes from the Languedoc dialect of the provençal language and means "masterly." The same wind is called mistrau in the occitan language, mestral in Catalan and maestrale in Italian and Corsican.
The mistral is usually accompanied by clear and sunny weather, and it plays an important role in creating the climate of Provence. It can reach speeds of more than ninety kilometers an hour, particularly in the Rhone Valley.
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[edit] The Cause of the mistral
The mistral is an example of a katabatic wind, which is created by the difference in pressure between the cold air of a high pressure system over the Atlantic or northwest Europe and a low pressure system over the Gulf of Lion or the Gulf of Genoa in the Mediterranean. The high-pressure air flows south through the Rhone Valley, gathering speed as it is funneled between the Alps and the Massif Central.
In France, the mistral particularly affects Provence, Languedoc east of Montpellier, and the department of the Var to the west of Frejus, as well as all of the Rhone Valley from Lyon to Marseille as far as Corsica and Sardinia. The mistral usually blows from northwest or north, but in certain pre-alpine valleys and along the Cote d'Azur, the wind is channelled by the mountains so that it blows from east to west. Sometimes it also blows from the north-north-east toward the east of Languedoc as far as Cap Béar. Frequently the mistral will affect only one part of the region, particularly when it is not caused by a flow of air from the northwest.
[edit] The mistral from the northwest
The mistral and the similar north wind in France, the tramontane, usually originate with a flow of air from the northwest. A cold front associated with a low pressure area over northern Europe moves toward the east. The flow shifts to the northwest, bringing with it cold maritime air. The cool wind from the northeast dries the air and rapidly disperses the clouds. The acceleration of the wind is caused by the creation of a depression, or low-pressure area, in the Gulf of Genoa under the wind from the Alps. In this case the mistral affects the entire Rhone Valley, the inland territory of Provence and the Cote d'Azur, where the wind comes from the east.
In the Languedoc area, where the tramontane is the strongest wind, the mistral and the tramontane blow together onto the Gulf of Lion and the northwest of the western Mediterranean, and can be felt to the east of the Balearic Islands, in Sardinia, and sometimes as far as the coast of Africa.
[edit] The mistral from the west
When the mistral originates from the west, the mass of air is not so cold and the wind only affects the plain of the Rhone delta and the Cote d'Azur. The good weather is confined to the coast of the Mediterranean, while it can rain in the interior. The Cote d'Azur generally has a clear sky and warmer temperatures, the classic effect of this type of Foehn Wind. This type of mistral usually blows for no more than one to three days.
[edit] The mistral from the northeast
The mistral originating from the northeast has a very different character; it is felt only in the west of Provence and as far as Montpellier, with the wind coming from either a northerly or north-northeasterly direction. In the winter this is by far the coldest form of the mistral, when it carries chill air from Central Europe and from Russia. It is caused by the presence of a high pressure area over northern Europe. The wind can blow for more than a week, until the high pressure area has moved east and the wind changes direction. This kind of mistral is often connected with a low pressure area in the Gulf of Genoa, and it can bring unstable weather to the Cote d'Azur and the east of Provence, sometimes bringing heavy snow to low altitudes in winter.
When the flow of air comes from the northeast due to a widespread low pressure area over the Atlantic and atmospheric disturbances over France, the air is even colder at both high altitudes and ground level, and the mistral is even stronger, and the weather worse, with the creation of cumulus clouds bringing weak storms. This kind of mistral is weaker in the east of of Provence and the Cote d'Azur.
[edit] The mistral from the east
The mistral is not always synonymous with clear skies. When a low pressure front over the Mediterranan approaches the coast from the southeast, the weather can change quickly for the worse, and the mistral and its clear sky changes rapidly to an east wind bringing humid air and threatening clouds. The position of the low-pressure front creates a flow of air from the northwest or the northeast.chanelled through the Rhone Valley. If this low-pressure area moves back toward the southeast, the mistral will quickly clear the air and the good weather will return; but if the cold-weather front continues to approach the land, bad weather will continue for several days in the entire Mediterranean basin, sometimes transforming into what French meteorologists call an épisode cévenol, a succession of torrential rains and floods, particularly in the areas west of the Rhone Valley: the Ardèche, the Gard, Herault and Lozère.
[edit] The summer mistral
The summer mistral, unlike the others, is created by purely local conditions. It usually happens in July, and only in the valley of the Rhone and on the coast of Provence. It is caused by a thermal depression over the interior of Provence (The Var and Alpes de Haute-Provence), created when the land is overheated. This creates a flow of air from the north toward the east of Provence. This wind is frequently cancelled out close to the coast by the breezes from the sea. It does not blow for more than a single day, but it is feared in Provence, because it dries the vegetation and it can spread forest fires
[edit] The Effects of the Mistral
[edit] Sunshine, clarity, and a dry climate
The mistral is a dry wind, and its arrival almost always clears the skies and dries the air. The Mistral helps explain the unusually sunny climate (2700 to 2900 hours of sunshine a year) and clarity of the air of Provence. When other parts of France have clouds and storms, Provence is rarely affected for long, since the mistral quickly clears the sky. In less than two hours, the sky can change from completely covered to completely clear. The mistral also blows away the dust, and makes the air particularly clear, so that during the mistral it is possible to see mountains 150 kilometers and farther away.
[edit] The mistral and health
The mistral has the reputation of bringing good health, since the dry air dries stagnant water and the mud, giving the mistral the local name mange-fange (eng. "mud-eater.") It also blows away pollution from the skies over the large cities and industrial areas.
[edit] The mistral and forest fires
The sunshine and dryness brought by the mistral have an important effect on the local vegetation. The vegetation in Provence, which is already dry because of the small amount of rainfall, is made even drier by the wind, which makes it particularly susceptible to fires, which the wind spreads very rapidly, sometimes devastating vast expanses of mountainside before being extinguished. During the summer, thousands of hectares can burn when the mistral is blowing.
[edit] The mistral and the growth of vegetation
In the Rhone Valley and on the plain of la Crau, the regularity and force of the mistral causes the trees to grow leaning to the south. Once the forest has been razed by fire, the strong wind makes it difficult for new trees to grow. The farmers of the Rhone Valley have long planted rows of cypress trees to shelter their crops from the dry force of the mistral. The mistral can also have beneficial effects- the moving air can save crops from the spring frost, which can last until the end of April.
[edit] Cooling of of the sea water
As summer visitors to the beach in Provence learn, the summer mistral can quickly lower the temperature of the sea, as the wind pushes the warm water near the surface out to sea and it is replaced by colder water from greater depths.
[edit] The effects of the mistral beyond France
The mistral can effect the weather in North Africa, Sicily and Malta or throughout the Mediterranean, particularly when low pressure areas form in the Gulf of Genoa.
The same name is used for the cool North/North-West wind in the Adriatic Sea. This is also a katabatic wind and has similar causes as its French namesake - air cooled over the Dinaric Alps flows down into the Adriatic sea, where it is known as Maestro or Maestral.
In south-western Crete it is known as Maestro and it is considered the most beneficial wind, which is said to blow only during the daytime.
[edit] The Mistral in Provençal Culture
The Mistral plays an important part in the life and culture of Provence, The Mas (Provencal Farmhouse) traditionally faces south, with its back to the Mistral. The bell towers of villages in Provence are often open iron frameworks, which allow the wind to pass through. The traditional Provençal Christmas crib often has a figure of a shepherd holding his hat, with his cloak blowing in the Mistral.
[edit] Sources and Citations
- ^ As defined in the French-language Wikipedia (see external links below)
- This article is largely an edited version of the articles from the French-language Wikipedia: Mistral (vent) and Vents de France.
- Jean Vialar, Les vents régionaux et locaux, 1948, republished by Météo-France in 2003
[edit] See also
- Bora (wind)
- Cers (wind)
- Etesian
- Gregale
- Khamaseen
- Levant (wind)
- Levantades
- Leveche
- Marin (wind)
- Sirocco
- Tramontane
- Winds of Provence
[edit] External links
- Meteo-France French-language on meteorology
- Article on Mistral from French Languge Wikipedia
- Local Mediterranean winds
- Name of Winds
