Wind speed is measured using an anemometer and is influenced by factors such as pressure gradients, local weather conditions, and Rossby waves. The Beaufort Scale is a standardized measure for wind speed, with ratings in knots, miles per hour and kilometers per hour.
Wind speed is typically judged as the speed of the wind. Most air movement measurements are taken from the outside air and there are several factors that can influence this. Average wind speed is often determined by an anemometer and is usually classified on a standardized measurement scale, called the Beaufort Scale.
Among the main factors affecting wind speed, the most important is called the pressure gradient, which is created by a graduated disparity in atmospheric pressure that occurs in different places. Some areas have low pressure, while others have higher pressure. For example, a valley may have a higher atmospheric pressure than a mountain peak that is a few miles away. Usually, the pressure gradually builds between both points.
For the most part, air moves along these pressure gradients from high pressure to low pressure. Motion is the main force that creates wind on Earth. The greater the pressure difference, the higher the wind speed. Therefore, areas that experience a large change in pressure over a short distance will typically have higher wind speeds than those where the change is more gradual.
Another factor that can affect wind speed is local weather conditions. Storm fronts often contribute to air currents, as they can create pressure gradients along which wind can travel. Freak storms, such as hurricanes or cyclones, can also drastically alter wind speed.
Another influence on wind speed is the presence of Rossby waves. These upper atmospheric air currents manipulate the weather patterns in the air below. They are caused by the Coriolis effect. A Ross wave can affect pressure gradients and increase velocities.
The most common way to measure wind speed is to use an anemometer. Early anemometers consisted of a vertical shaft with a horizontal spoke wheel. Each spoke holds a small cup at its end and the cups catch the wind to spin the wheel. Wind speed can be calculated based on how often the wheel rotates in a given period of time. Many of these devices are still made this way.
Other types of anemometers have also been developed. Laser Doppler anemometers use lasers to calculate wind speed. Windmill anemometers work with a fan pointing into the wind. Hot wire anemometers use the friction produced by the wind on an electrically charged wire to determine wind speed.
The Beaufort scale is a standardized measure for wind speed. It is an empirical evaluation system originally based on the appearance and height of the waves at sea. The system was developed to also include speed ratings for each level in knots, miles per hour and kilometers per hour.
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