wind

Engineers are shown testing a propeller in a subsonic wind tunnel. Aerodynamic studies in wind tunnels have been important in solving design problems in aircraft, spacecraft, cars, boats, trains, bridges, and building structures.

Lateral movement of the Earth's atmosphere from high-pressure areas (anticyclones) to low-pressure areas (depressions). Its speed is measured using an anemometer or by studying its effects on, for example, trees by using the Beaufort scale. Although modified by features such as land and water, there is a basic worldwide system of trade winds, westerlies, and polar easterlies.

A belt of low pressure (the doldrums) lies along the Equator. The trade winds blow towards this from the horse latitudes (areas of high pressure at about 30° north and south of the Equator), blowing from the northeast in the northern hemisphere, and from the southeast in the southern hemisphere. The westerlies (also from the horse latitudes) blow north of the Equator from the southwest, and south of the Equator from the northwest.

Cold winds blow outwards from high-pressure areas at the poles. More local effects result from landmasses heating and cooling faster than the adjacent sea, producing onshore winds in the daytime and offshore winds at night.

The monsoon is a seasonal wind of southern Asia, blowing from the southwest in summer and bringing the rain on which crops depend. It blows from the northeast in winter.

Famous warm winds include the chinook of the eastern Rocky Mountains, North America; the föhn of Europe's Alpine valleys; the sirocco (Italy)/khamsin (Egypt)/sharav (Israel) – spring winds that bring warm air from the Sahara and Arabian deserts across the Mediterranean; and the Santa Ana, a periodic warm wind from the inland deserts that strikes the California coast.

The dry northerly bise (Switzerland) and the mistral (which strikes the Mediterranean area of France) are unpleasantly cold winds.

The fastest wind speed ever measured on Earth, 512 kph/318 mph, occurred on 3 May 1999 in a tornado that struck the suburbs of Oklahoma City, Oklahoma, USA.