Movement of air is known as wind. It can flow from any direction from horizontal to vertical depending on the energy balance. Wind can also curve or even rotate. Examples of rotating air are tornadoes and dust devils.

Wind speed and direction is measured by anemometers which vary in accuracy. The units of measurement for wind speed is normally km/hr (kilometres per hour). Direction of wind is determined as a bearing angle from N. It is sufficient to use the eight points of the compass as a basis for determination of wind direction. Wind direction is noted from where it approaches, not where it is heading. There are many different types of instruments that measure wind speed and direction. However, the most common instrument used is known as an anemometer. It consists of three cups on arms that can rotate measuring wind speeds based on rate of rotations and a vane which indicates the wind direction.

Trees are an efficient form of estimating wind strength. Flexible trees such as the weeping willow is good for lighter wind conditions whilst trees with stronger, less flexible branches sway during moderate to strong winds. Once wind reaches the strong to gale force category, damage to trees begin to occur such as broken twigs, branches and removal of leaves. The Beaufort scale incorporates these measurement techniques and other effects into certain ranges of wind strength estimates.

[ Images above ] Fresh Breeze: Small trees like this birch ( right) sway. [ Location: Oberdiessbach, Switzerland ]

Wind can also create sound. Wind passing around an object causes vibrations of that object that in turn creates a sound, normally a hissing or howling sound. We tend to perceive wind strengths based on certain sounds but mainly because we have really associated these sounds with the wind effects on objects.

The movement of fast moving low clouds normally indicates the approximate direction of the wind. Fog also will move in the direction of the wind.

Wind can raise dust and other light objects and therefore following, this movement is yet another technique that can help you estimate the strength and direction of the wind. It also can reveal eddies created by objects as wind flows around them. The same technique applies for blowing snow but this normally requires higher wind speeds.

If you are near or on a lake or ocean, it is possible to observe surface flow of wind based on the changes in water texture or ripples. Relatively stronger winds will disturb the water surface causing ripples. This region of ripples or darker texture can be observed moving as the wind progresses. Therefore, if this region passes over your location, you will experience stronger winds. This technique is widely used by sailors. Wind can also create waves with heights that vary according to the wind speed.

There are probably other techniques not discussed here that can be used to observe wind. However, what has been discussed indicates various approaches that directly relate to more immediate wind effects.

THE BEAUFORT WIND SCALE

One of the first scales to estimate wind speeds and the effects was created by Britain's Admiral Sir Francis Beaufort (1774-1857). He developed the scale in 1805 to help sailors estimate the winds via visual observations. The scale starts with 0 and goes to a force of 12. The Beaufort scale is still used today to estimate wind strengths.

Specifications and equivalent speeds for use on land

BEAUFORT SCALE: Specifications and equivalent speeds for use at sea.

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