From Wikipedia, the free encyclopedia
Wind, from the Tacuinum Sanitatis, late 14th century (Biblioteca Casanatensis, Rome).
Wind is the flow of air or other gases that compose an atmosphere (including, but not limited to, the Earth’s). Wind is air molecules in motion on Earth, and in the case of the solar wind, the movement of charged particles from the sun through space. Differences in density between two air masses lead to wind. Differential heating between the poles and the equator lead to the development of the jet stream and the associated climatological mid-latitude westerlies, polar easterlies, and the trade winds. Winds are commonly classified by their spatial scale, their speed, the types of forces that cause them, the geographic regions in which they occur, and their effect. Wind speeds over much of the globe are measured over a ten-minute time frame, except the United States which uses a two-minute average. Winds are plotted on surface weather analyses within station models, indicating the direction the wind is blowing from as well as its strength.
Wind speeds have various names associated with their average strength, such as breeze, gale, storm, hurricane, and typhoon. Wind gusts exceed the minimum value over the observed time frame. Winds which sharply increase and last for a minute are termed squalls. While wind is often a standalone weather phenomenon, it can also occur as part of a storm system, most notably in a cyclone. Winds can shape landforms, via a variety of aeolian processes. Wind occurs on a range of scales, from local breezes generated by heating of land surfaces and lasting tens of minutes, to global winds resulting from the difference in absorption of solar energy between the climate zones on Earth. The two major driving factors of large scale atmospheric circulation are the differential heating between the equator and the poles, which causes the jet stream, and the rotation of the planet (Coriolis effect) which causes the circular motion of air around areas of high and low pressure.
In human civilization, wind has inspired mythology, changed the course of history, expanded the range of transport and warfare, and provided a power source for mechanical work, electricity, and recreation. Wind has been used to steer sailing ships across vast oceans. By air, hot air balloons use the wind to take short trips. Airships have historically been used for longer trips, but nowadays are used for a variety of monitoring efforts such as during public sporting events and drug trafficking efforts. Areas of wind shear caused by various weather phenomena can lead to dangerous situations for airplanes. Nature uses wind to help disperse seeds from various plants, in order to enable the survival of those plant species. Dust from large deserts can be moved large distances from their source region by the prevailing winds.