Wind

Wind is the flow of air. More generally, it is the flow of the gases which compose an atmosphere; since wind is not only an Earth based phenomenon.

There are global winds, such as the wind belts which exist between the atmospheric circulation cells. There are upper-level winds which typically include narrow belts of concentrated flow called jet streams. There are synoptic-scale winds that result from pressure differences in surface air masses in the middle latitudes, and there are winds that come about as a consequence of geographic features, such as the sea breezes. Mesoscale winds are those which act on a local scale, such as gust fronts. At the smallest scale are the microscale winds, which blow on a scale of only tens to hundreds of meters and are essentially unpredictable, such as dust devils and microbursts.

Forces which drive wind or effect it are, the pressure gradient force, the Coriolis force, bouyancy forces, and friction forces. When a difference in pressure exists between two adjacent air masses, then air tends to flow from the region of high pressure to the region of low pressure. On a rotating planet, flows will be acted apon by the Coriolis force, in regions sufficiently far from the equator and sufficiently high above the surface.

The two major driving factors of large scale global winds are the differential heating between the equator and the poles (difference in absorption of solar energy between these climate zones), and the rotation of the planet.