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Wind
A gentle breeze cools the home on a hot
summer day. A colorful kite floats high above the heads of a picnicking
family at play. The tinkling of chimes beneath a baby's bedroom window
lulls the infant to sleep. With sails unfurled, a sailboat races toward
the horizon. The wind is friend.
A hurricane roars
inland, destroying homes and communities. Without warning, a thunderstorm
rolls into town, dampening picnic plans. The slamming of shutters outside
a baby's bedroom window shatters the infant's sleep. Surf's up, and the
waves pound wickedly, whipping the sailboat toward the rocks. The wind is
fierce. Enemy or ally? Friend or foe? Our relationship with the wind is
often uncertain.
The air of our atmosphere moves in many
directions and at varying speeds. It can be as gentle as a spring breeze
or as dangerous as a tornado. But did you ever wonder about wind? What
forces cause air to move? What would Earth's environment be like without
the global and local circulation of wind?
Air is a fluid which moves in circuits, powered
by unequal heating of large masses of air. As the Earth's surface is
warmed differentially, the air above these surfaces absorbs different
amounts of heat. Warmer air rises while cool air sinks which creates the
environment for flowing air movement. Winds flow across parallels of
latitude, taking heat from equatorial regions to polar regions. This
equalizing process causes wind and is of major importance in determining
the environments for life on land, global as well as local weather
patterns, and a clean, inexpensive source of energy for humans.
Wind is air that is in motion relative to the
rotating surface of the Earth. Any wind possesses a three-dimensional
structure - that is, it has both horizontal and vertical components. The
horizontal components, however, are considerably greater than the vertical
ones. A fairly typical horizontal wind speed might be 50 km/h (31.25 mph).
Vertical wind speeds are usually measured only in tenths of a kilometer
per hour. Consequently, the term wind has become synonymous with the
horizontal components of the winds.
In meteorology and in common usage, the
location from which the wind blows is used to indicate the wind's
direction. For example, a so called northwesterly wind is one that blows
from the northwest.
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