At the equator, the sun’s
heat warms the air. In
this area, the air rises,
causing a belt of
calm air called
the doldrums.569
World Winds
Besides local and seasonal winds, there
are certain winds that always blow. These are
called prevailing winds. There are three main belts
of prevailing winds on each side of the equator. They are
called the trade winds, the westerlies, and the polar easterlies.
The direction they blow in is affected by the spin of Earth.
They are angled toward the left in the southern Hemisphere
and toward the right in the northern Hemisphere.Wind dirEcTion
A wind is often named according
to the direction from which it is
coming. For example, a wind
that comes from the west is
called a westerly. Windsocks
(above) and vanes are used to
show wind direction.Monsoons
seasonal winds that blow in a
particular direction are called
monsoons. For example, during
the summer in southern Asia, the
wind blows from the indian
ocean toward the land, bringing
heavy rains. in the winter the
wind blows in the opposite
direction, from the Himalayas
toward the ocean.As A gEnTlE BrEEzE or a powerful hurricane, wind blows constantly
around the world. Winds are belts of moving air that flow from one area
to another, driven by the sun’s heat. Warm air is lighter than cold air, so
warm air rises as it is heated by the sun, and cold air flows in to take its
place. This sets up a circular current of air which produces winds. light,
warm air exerts less pressure on Earth than cold air, creating an area of
low pressure toward which cold air flows. similarly, cold air sinks and
produces an area of high pressure from which air flows outward. The
greater the difference in pressure between two areas, the stronger the winds.
Weather forecasters use the Beaufort scale to measure the speed of wind.
it runs from 0 to 12: for example, force 2 is a light breeze; force 12 is
a hurricane. The size and shape of areas of land
and water affect local winds, which are
often given special names, such as the
chinook in north America and
the sirocco in italy.Wind
Wind turbines
The earliest ships used wind power to carry them
across the sea. Wind also powers machines.
Windmills were used in iran as long ago
as the 7th century for raising water from
rivers, and later for grinding corn. Today,
huge windmills, or wind turbines, can
produce electricity; a large wind turbine
can supply enough electricity for a small
town. Wind turbines cause no pollution,
but they are large and noisy and take
up huge areas of land.The polar easterlies
are cold winds
which blow away
from the poles.A wind farm in the United
States uses 300 wind turbines
to produce electricity.When the air has risen
very high, it cools and
sinks back to Earth in
the horse latitudes.WesterliesHorse latitudesWesterliesNE trade
windsEquatorSE trade
windsHorse latitudesPolar easterliesThe trade winds flow from
the horse latitudes toward
the equator.In between the westerlies and
the trade winds is an area of
calm called the horse latitudes.
The name may refer to the many
horses that died on ships that
were becalmed in this region.Horse latitudesHorse latitudesDoldrumsDoldrumsPath of airPath of airFind out more
climates
Energy
storms
WeatherThe westerlies are warm
winds that blow away from
the horse latitudes in the
direction of the poles.US_569_Wind.indd 569 27/01/16 2:40 pm