"W I N D"
Causes of the wind...If the temperature were the same everywhere on
the surface of the earth, then the air would have the same density
everywhere at the same level and there would be no tendency for it to
move from one place to another, there would be no wind. The primary cause
of winds, therefore, is the difference in temperature.
Wind may be defined as air in motion. It is usually described as air
moving as a body, large or small, in a generally horizontal direction.
When air moves vertically it is call a current.
Heated air will be bouyed up by the surrounding denser air and will
rise. Such a rising current (Thermal), reduces pressure at a given locality.
The surrounding denser, cooler, heavier air (High Pressure), will move
horizontally to replace the rising warmer, lighter air. )Low Pressure).
By this process a flow of air develops (Wind), from higher pressure to lower
pressure, caused by the difference in temperature.
The definition of wind as the motion of air and the invention of the
windvane go back before the Christian era. It was recognized by the Greeks
that the different types of weather were associated with winds from different
directions.
"Observing And Estimating Wind"
The direction of wind is measured in the horizontal plane and is easily
indicated by a weather vane which points in the direction from which the air
is flowing past.
The direction of the wind is reported either by the point of the compass,
(true direction), from which the wind blows, or by its Azimuth in degrees in the
same way as the hands of a clock is said to be Veering, and one which changes in
the reverse direction is said to be Backing.
The observation of the wind force offers more difficulty and estimates are based
on the effect of the wind on movable objects. Almost anything which is supported so
that it is free to move under the influence of the wind can be used.
The instrument most widely used by the National Weather Service measure wind
speed, is call an Anemometer. It consists of three cups which are extended about a
vertical axis. The cups revolve as the wind blows. An electrical contact is made
and transmitted to a meter inside the Weather Office where the observations are made.
In the days of Iron Men and Wooden Ships, sailors depended upon their skills for
their motion and estimates of the force of the wind.
A scale was first put into numerical form by Sir Frances Baufort, an Admiral and
Hydropgrapher in the British Royal Navy, in the year 1806, but was not adopted for use
on land until 1906. A sequence of 12 grades of wind was enumerated from 0. flat calm,
to 12, the force of a hurricane and is still in use today as the Beaufort Wind Scale.
"Weather By Giannetta"
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