Wind speed

Wind speed is the speed of wind, the movement of air or other gases in an atmosphere. It is a scalar quantity, the magnitude of the vector of motion.

Wind speed has always meant the movement of air in an outside environment, but the speed of air movement inside is important in many areas, including weather forecasting, aircraft and maritime operations, building and civil engineering. High wind speeds can cause unpleasant side effects, and strong winds often have special names, including gales, hurricanes, and typhoons. See the Beaufort scale.

Speed and velocity
Technically, wind speed is given by


 * $$|\mathbf{v}|=\sqrt{u^2+v^2+w^2}$$,

where u, v, and w are zonal, meridional, and vertical components of wind velocity. Except in unusual circumstances (e.g. in cumulus updrafts), the vertical component of the velocity is much smaller than the horizontal components.

Factors affecting wind speed
Wind speed is affected by a number of factors, situations, operating on varying scales (from micro to macro scales). These include the pressure gradient, Rossby waves and jet streams and local weather conditions. There are also links to be found between wind speed and wind direction, notably with the pressure gradient and surfaces that the air is to be found over.

Pressure gradient is a term to describe the difference in air pressure between two points in the atmosphere or on the surface of the Earth. It is vital to wind speed, because the greater the difference in pressure, the faster the wind flows (from the high to low pressure) to balance out the variation. The pressure gradient, when combined with the Coriolis Effect and friction, also influences wind direction

Rossby waves are strong winds in the upper troposphere. These operate on a global scale and move from West to East (hence being known as Westerlies). The Rossby waves are themselves a different wind speed to what we experience in the lower troposphere.

Local weather conditions play a key role in influencing wind speed, as the formation of hurricanes, monsoon or cyclones as freak weather conditions can drastically affect the velocity of the wind.

Highest speed
The highest surface wind speed ever officially recorded is 372 km/h (231 mph) at the Mount Washington (New Hampshire) Observatory in the US on 12th April 1934, using a heated wire anemometer. The anemometer was later tested by the US National Weather Bureau and confirmed to be accurate. The highest surface wind speed ever officially recorded in Asia was recorded in Afghanistan on 14 August, 2008: 328 km/h (204 mph) in Ab-Paran, Ghowr.

A higher windspeed recorded at 380 km/h (236 mph) during Typhoon Paka in 1997 in Guam was declared invalid because the instrument was damaged during the storm and could not later be checked for accuracy.

Windspeeds within certain atmospheric phenomena (such as tornadoes) may greatly exceed this value but have never been accurately measured. The figure of 509 km/h (316 mph) during the F5 tornado, Moore in Oklahoma, USA is often quoted as the highest surface wind speed but was measured 30 m (100 feet) above ground.