Wind

[admin (Simon W)]

What is wind?

Wind is simply air in motion, moving from high pressure to low pressure. Winds are described by the direction they blow from - an easterly wind lows from the east, a westerly from the west. Prevailing winds (winds which occur frequently in a particular direction) are arranged in a series of belts around the globe. This pattern is the result of differences in the speed the Earth rotates and the different amounts of solar heating it gets, depending on where a place is between the poles and the equator.

There are many smaller scale winds and wind patterns produced by a number of processes. Mountains often produce their own local winds, and wind currents can be shaped as they are forced to rise or funnelled through valleys, greatly increasing their strength. As an air mass descends a mountain slope it is compressed and becomes a warm dry wind. The effect is most noticeable in spring when these winds can melt snow very quickly. They are called föhn winds in the Alps and chinook ("snow-eaters") in western North America and they can sometimes cause avalanches.

Local Winds have names

Other winds are truly local and are caused by a daily pattern of air-flow up and down valleys.

Katabatic winds occur at night when cool air sinks down mountain slopes and valleys.

Anabatic winds occur when sun-warmed air rises and gently flows up mountain slopes and valleys.

Local winds in different countries have special names and often have particular characteristics associated with them, such as the Mistral - a dry and cold wind common to the Rhone Valley in France.

Under hot sunshine, thermals can rise very strongly and produce short-lived whirlwinds. These dust-devils or sand-devils are a fairly common sight on sunny days in dry, open country and can send a Paraglider into a swirling mess that takes a day to untangle!.

Intense heating of a patch of ground by the Sun may create a spiralling column of hot air that can reach more than 100 m (330 ft) in height. Lightweight material, such as dust or a paraglider , is lifted up and briefly whirled around. Whirlwinds rarely last more than a few minutes after which the air column gently collapses.

Please feel free to add to this thread.

[norman]

For those new to flying.

Laminar flow is an expression you might hear used at the flying field. The holy grail of kiting sessions and early paramotor launches, laminar flow makes the job so much easier.

Simply put it is smooth, constant flow with no ripples or undulations contained within. See this video (ignore the first part) to watch laminar flow striking different surface forms to get an impression of what 'laminar' means.

Hold the images in your mind and apply them to your visualization of what happens to air when it strikes trees or any obstructions.

The result is the tumbling rotor that makes kiting difficult and flying under a parachute challenging. 'Non Laminar' flow.

You might ask yourself where would you find some of the best laminar wind flow? That would be the place to go for early kiting practice. Look out for loonies tho'. Still, you could always try Scotland.

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