By definition, wind is a meteorological phenomenon corresponding to the movement of an air mass from an area of high pressure to an area of low pressure. It moves as a result of local differences in temperature and pressure.
The wind plays a real role, since it is the main actor of the oxygenation of the oceans, of the mountain lakes, through the agitation and the setting in movement of these surfaces. It also allows the movement of organic and mineral agents, explaining the formation of certain rocks. It also influences the movement of flying insects, the migration of birds and the formation and reproduction of certain plants.
The formation of wind at the Earth's surface is linked to two parameters: temperature and pressure. When an air mass heats up under the effect of the sun's rays, for example, or when it comes into contact with a hot environment. Indeed, the sun heats the seas and continents which then heat the air above them. This air mass therefore becomes lighter and rises in altitude above the colder layers. This movement creates a depression. Conversely, the air mass cools and descends, creating an area of high pressure. During this movement, the cold air that descends meets the warm air that rises. The difference in pressure and temperature between these two air masses is ultimately responsible for creating the wind. The higher this difference is, the stronger the wind will be.
Wind is characterized by the measurement of two quantities: the direction and the speed.
In order to measure its direction, we use a wind vane. It is a plate of variable shape, mobile around a vertical axis, placed above a roof or a mast. Under the effect of the wind, the instrument is placed in the direction of the wind, thus giving its direction.
Concerning the speed, the instrument used is the anemometer which is used, in general, to measure the speed of a gaseous fluid.
Regarding the speed, scales have been established in order to estimate the intensity of winds.
The Beaufort Scale: Invented in 1805 by Francis Beaufort, a British admiral, it ranges from 0 to 12 and is based on the average wind speed over a 10-minute period. Level 0 corresponds to zero wind intensity. The level 12 corresponds to a very violent wind, classified as a hurricane.
Fujita Scale: This scale was developed by Theodore Fujita and Allan Pearson in 1971 and was based on the damage caused. It is spread over 6 levels from F0 "slight damage" to F5 "incredible damage".
Four families of winds can be identified :
- Planetary winds, with large-scale movement, affecting vast regions of the globe.
- Cyclonic disturbances, with a medium-scale movement, linked to the meeting of great cold and great heat.
- Local winds with small-scale motion, affecting limited regions.
- Atmospheric turbulence on a small scale, acting on small portions of territory.
Here are some wind records from around the world.
In 2010, the WMO (World Meteorological Organization) certified Cyclone Olivia hitting Barrow Island in Western Australia in 1996 as the strongest wind record ever observed scientifically on Earth outside of tornadoes. Indeed, during this episode, a gust of 408 km/h was recorded, with a maximum sustained wind of 230 km/h over 1 minute.
A series of tornadoes (66 in total) touched down in this south-central U.S. state, where a mobile weather radar recorded winds of 484 km/h (with a margin of error of plus or minus 30 km/h). An F5 tornado struck Moore and Bridge Creek, two Oklahoma communities, overnight. A tornado traveled more than 50 km causing 46 deaths, 800 injuries and 8,000 destroyed homes, with an estimated damage of $1.5 billion.
Records have been set in the high mountains. A gust of 360 km/h at Mont Aigoual in 1968, and 320 km/h at Mont Ventoux in 1967.