Wind speed
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Wind speed is the speed of movement of air relative to a fixed point on the earth. It usually means the movement of air in an outside environment, but the speed of movement of air inside a building or structure may also be referred to as 'wind speed'.
Wind speed 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. Wind speed can affect sporting achievements either beneficially or adversely. Most outdoor sports have limits of windspeed outside of which records are considered invalid.
Units of measurement
Windspeeds may be measured in a variety of standard units of speed. Metres per second is common for scientific purposes. Miles per hour or kilometres per hour is often used for common weather reporting; aeronautical or maritime reports may use those or knots (nautical miles per hour).
Other empirical scales exist: the Beaufort scale is a common way to assess wind speed without an anemometer, and is often used in maritime weather reports and forecasts. The Fujita scale allows classification of tornadoes in six categories.
Wind speed is the speed of movement of air relative to a fixed point on the Earth.
Measuring windspeed
Wind speed may be measured by a variety of tools. The anemometer, consisting of a rotating vane, has been the most common method of measuring speeds close to the ground for hundreds of years. The aviation windsock is used by pilots to give information on wind direction and approximate speed for relatively low speeds. Weather balloons are used to find windspeed at high altitudes - they are released into the high atmosphere and tracked using radar or radio, their speed giving the windspeed at that position.
Pilots of aircraft can also estimate windspeed from their own position. Aircraft position is affected both by its movement through the air and the movement of the air relative to the earth, a pilot who can fix his position relative to the ground and knowing from instruments his movement through the air can estimate the wind speed and direction over the time he has been flying. Such reports can be used to confirm wind speed forecasts. The development of accurate electronic navigation systems, including inertial navigation and GPS enable this calculation to be done automatically. Modern GPS and inertial systems often include a direct readout of the current windspeed and direction.
Speed and Velocity
Technically Wind speed is given by
- <math>|\mathbf{v}|=\sqrt{u^2+v^2+w^2}<math>,
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 component.