‘Wind’ is the word used to describe the movement of air across the Earth’s surface. Air is constantly moving and is influenced by temperature and pressure.
When one area of air heats up more than the area next to it, a difference in pressure occurs and this creates wind. When air heats up it rises, and colder air moves into replace it. As the rising air begins to cool it descends. The rising air underneath cannot descend and is therefore pushed to the side. This is how wind is created.
As different parts of the earth are heated differently, different areas of pressure occur. These changes in pressure vary between the equator and the poles; between the land and the sea as well as changing between day and night. All of these can cause pressure variations. Additionally, the rotation of the Earth causes pressure variations along the atmosphere due to the Coriolis Effect.
Wind strength is measured in speed and is classified using the Beaufort scale. In addition to the speed of the wind, the Beaufort scale also considers descriptive terms which describe the conditions on the land and sea:
Direction is used to describe the winds movement. Wind direction describes the direction from which the wind is blowing compared to North. Eight principle wind directions are used to record this along with an additional eight secondary directions. The wind directions are represented on a compass, or wind, rose. Below, is an example of a compass rose representing all the principal and secondary winds and a table including the principal winds, their abbreviations and their traditional names.
|North-East||NE||45°||Greco or Grecale|
|South||S||180°||Ostro or Mezzogiorno|
|South-West||SW||225°||Libeccio or Garbino|
|North-West||NW||315°||Maestro or Mistral|
Temperature variations impact both wind’s speed and direction while, the Coriolis Effect only impacts the wind’s direction.
Several instruments are used to measure wind speed and direction.
One common instrument used to display wind direction is the weather (or wind) vane. These are usually found on the roofs of high buildings. They are designed so that they always point in the direction that the wind is blowing from.
Another instrument that indicates both wind speed and direction is the wind sock. This is widely used in open areas, such as airports and seaports, where it is used to visually depict wind characteristics. The shape and movement of a wind sock indicates the wind intensity while the direction of the sock indicates the direction the wind direction.
Whilst a wind sock gives a visual estimate of wind speed, a precise recording of wind speed is often required. Instruments called anemometers, which measure the wind speed directly, are used for this purpose. The simplest and most common type of anemometer consists of hemispherical cups, which spin around according to the strength of the wind and are placed vertically on a base and a recording device. The device counts the cups’ rotations in a given time and calculates the wind speed.
More advanced types of anemometers that measure the wind speed directly include: windmill anemometers; hot-wire anemometers; laser Doppler anemometers; sonic anemometers and ping-pong ball anemometers. There are additional anemometers which also measure air pressure along with wind speed.
Wind speeds can also be measured by instruments placed on airplanes and satellites.
Wind has played an influential role throughout human history by allowing movement and technological advances. Wind was used to power early sail boats and this method of transport is still used today. By harnessing the wind in this way humans have been able to explore the world and develop trade and commerce.
Wind has also been used to drive technology for centuries, with one of the oldest wind powered devices being the wind wheel of Heron of Alexandria (Hero Of Alexandria Engine).
One of the most common wind powered inventions seen today is the windmill. Initially, windmills were used for grinding seeds for food production. Windmills have since evolved and are now used in many industries. Today, windmills are most commonly used to pump water, either for land drainage or to extract groundwater.
In recent years windmills have evolved further and wind turbines are now used to generate electricity. Wind turbines can be used to produce electricity for a single home or building, or they can be connected to an electricity grid and provide electricity over a wider area. In order to generate large amounts of electricity many wind turbines are placed together. These are known as windfarms. To maximize efficiency windfarms are placed in extremely windy areas. This can be either on land or at sea.