Mistral (Wind)

Mistral (wind) a week.[5] 1 The cause of the mistral Mistral wind blowing near Marseille. In the centre is the Château d'If The mistral (Catalan: Mestral, Greek: Μαΐστρος) is a strong, cold, northwesterly wind that blows from southern France into the Gulf of Lion in the north- ern Mediterranean, with sustained winds often exceeding forty kilometers per hour, sometimes reaching one hun- dred kilometers per hour.[1] It is most common in the win- A map showing the force of the mistral one day in November ter and spring, and strongest in the transition between the 2008. The wind reached a speed of 80 km/h (50 mph), with two seasons. Periods of the wind exceeding thirty kilo- average speeds of more than 50 km/h (31 mph) an hour near meters an hour for more than sixty-five hours have been Marseille. reported.[2] The mistral takes place each time there is an anticyclone, In France, it refers to a violent, cold, north or northwest or area of high pressure, in the Bay of Biscay, and an area wind that accelerates when it passes through the valleys of low pressure around the Gulf of Genoa. When this of the Rhone and the Durance Rivers to the coast of the [3] happens, the flow of air between the high and low pres- Mediterranean around the Camargue region. It affects sure areas draws in a current of cold air from the north the northeast of the plain of Languedoc and Provence to which accelerates through the lower elevations between the east of Toulon, where it is felt as a strong west wind. It the foothills of the Alps and the Cevennes. The condi- has a major influence all along the Mediterranean coast of tions for a mistral are even more favorable when a cold France, and often causes sudden storms in the Mediter- rainy front has crossed France from the northwest to the ranean between Corsica and the Balearic Islands.[4] southeast as far as the Mediterranean. This cold, dry wind The name mistral comes from the Languedoc dialect of usually causes a period of cloudless skies and luminous the Occitan and means “masterly”. The same wind is sunshine, which gives the mistral its reputation for mak- called mistrau in the Provençal variant of Occitan, mestral ing the sky especially clear. There is also, however, the in Catalan, maestrale in Italian and Corsican, maistràle or mistral noir, which brings clouds and rain. The mistral bentu maestru in Sardinian, and majjistral in Maltese. noir occurs when the Azores High is extended and draws [5] The mistral is usually accompanied by clear, fresh in unusually moist air from the northwest. weather, and it plays an important role in creating the The long and enclosed shape of the Rhone Valley, and climate of Provence. It can reach speeds of more than the Venturi effect of funnelling the air through a narrow- ninety kilometers an hour, particularly in the Rhone Val- ing space, is frequently cited as the reason for the speed ley. Its average speed during the day can reach about fifty and force of the mistral, but the reasons are apparently kilometers an hour, calming noticeably at night. The mis- more complex. The mistral reaches its maximum speed tral usually blows in winter or spring, though it occurs in not at the narrowest part of the Rhone Valley, south of all seasons. It sometimes lasts only one or two days, fre- Valence, but much farther south, where the Valley has quently lasts several days, and sometimes lasts more than widened. Also, the wind occurs not just in the Valley, 1 2 2 THE EFFECTS OF THE MISTRAL but high above in the atmosphere, up to the troposphere, is not so cold and the wind only affects the plain of the three kilometres (1.9 miles) above the earth. The mis- Rhone delta and the Côte d'Azur. The good weather is tral is very strong at the summit of Mont Ventoux, 1900 confined to the coast of the Mediterranean, while it can meters in elevation, though the plain below is very wide. rain in the interior. The Côte d'Azur generally has a clear Other contributing factors to the strength of the mistral sky and warmer temperatures. This type of mistral usu- are the accumulation of masses of cold air, whose volume ally blows for no more than one to three days. is greater, pouring down the mountains and valleys to the The mistral originating from the northeast has a very dif- lower elevations. This is similar to a foehn wind, but un- ferent character; it is felt only in the west of Provence and like a foehn wind the descent in altitude does not signif- as far as Montpellier, with the wind coming from either a icantly warm the mistral. The causes and characteristics northerly or north-northeasterly direction. In the winter of the mistral are very similar to those of the Tramontane, [6] this is by far the coldest form of the mistral. The wind can another wind of the French Mediterranean region. blow for more than a week. 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 Côte 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 atmo- spheric 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 Provence and the Côte d'Azur. The mistral is not always synonymous with clear skies. When a low pressure front over the Mediterranean ap- proaches 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, channeled 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 re- turn; but if the cold-weather front continues to approach the land, bad weather will continue for several days in the The bell tower of the hilltop village of La Cadière-d'Azur is open, entire Mediterranean basin, sometimes transforming into which allows the mistral to pass through. what French meteorologists call an épisode cévenol, a suc- cession of torrential rains and floods, particularly in the areas west of the Rhone Valley: the Ardèche, the Gard, In France, the mistral particularly affects Provence, Hérault and Lozère.[7] Languedoc east of Montpellier, as well as all of the Rhone Valley from Lyon to Marseille, and as far southeast as The summer mistral, unlike the others, is created by Corsica and Sardinia. The mistral usually blows from purely local conditions. It usually happens in July, and the north or northwest, but in certain pre-alpine valleys only in the valley of the Rhone and on the coast of and along the Côte d'Azur, the wind is channelled by the Provence. It is caused by a thermal depression over mountains so that it blows from east to west. Sometimes the interior of Provence (The Var and Alpes de Haute- it also blows from the north-north-east toward the east of Provence), created when the land is overheated. This Languedoc as far as Cap Béar. Frequently, the mistral creates a flow of air from the north toward the east of will affect only one part of the region. Provence. This wind is frequently cancelled out close to the coast by the breezes from the sea. It does not blow for In the Languedoc area, where the tramontane is the more than a single day, but it is feared in Provence, be- strongest wind, the mistral and the tramontane blow to- cause it dries the vegetation and it can spread forest fires. gether 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. When the mistral blows from the west, the mass of air 2.1 The effects of the mistral beyond France 3 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. 2.1 The effects of the mistral beyond France 2 The effects of the mistral The mistral helps explain the unusually sunny climate Oak bent to the south by the mistral in Sardinia (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 The mistral can affect the weather in North Africa, Sicily mistral quickly clears the sky. In less than two hours, the and Malta or throughout the Mediterranean, particularly sky can change from completely covered to completely when low-pressure areas form in the Gulf of Genoa. 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 kilometres (93 miles) and 3 Maestral or maestro in the Adri- farther away.

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