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Earth^51

Winds are moving currents of air,

which can blow over a small local

area or over a much larger region.

Global winds help to moderate

temperatures worldwide by carrying

warm air away from the tropics and

cold air from the poles. Winds bring

changing weather conditions, such

as clear, sunny skies or torrential

. MONSOON rain. Strong winds

can bring storms and hurricanes.

WHAT FORCES AFFECT THE WORLD’S WINDS?

Regular wind patterns across the Earth’s surface are

affected by the planet’s spin. This is called the Coriolis

Effect. In the northern hemisphere, the Coriolis Effect

causes winds to swirl clockwise. In the

southern hemisphere, it causes winds

to spin anticlockwise. The speed and

direction of the wind is also affected

by air currents blowing over natural

features, such as mountains.

Monsoon winds are massive winds that

bring heavy, seasonal rain to subtropical

regions, such as southeast Asia and India,

in summer. In winter, they bring dry, cooler

weather. Monsoon winds are the strongest

in Asia, but they also blow in West Africa,

northern Australia, and parts of North

and South America.

WHY DO MONSOONS CHANGE DIRECTION?

Monsoon winds change course because of seasonal

temperature differences between the land and the sea.

Water absorbs heat more slowly than dry land but

holds the heat for longer. This makes the sea cooler

than the land during the summer, and warmer during

the winter. The difference in temperature causes

monsoon winds to blow onshore (from sea to land) in

summer, and offshore (from land to sea) in winter.

WHY DO WINDS BLOW?

Winds are caused by the Sun heating air masses in

different parts of the world unevenly. Air warmed by

the Sun becomes less dense, or lighter, and rises. This

creates an area of low pressure where there is less air

pressing down on the Earth. Because air always flows

from a region of high pressure to one of low pressure,

cooler air flows in to fill the space left by the rising

air. This is a wind.

GLOBAL WINDS

Three main belts, or bands, of prevailing winds blow on either side

of the Equator. In the Tropics, trade winds blow from the northeast

or southeast towards the Equator. In temperate zones, the

prevailing winds are westerlies (blowing from the west). Cold,

easterly winds (from the east) blow in the polar regions.

1 MONSOON RAIN

The monsoon brings much-needed water to regions such as Bangladesh,

in Asia, after a long, dry season. Sometimes, the rains are too heavy,

washing away crops and homes and causing widespread flooding.

4 WINDY WEATHER

Light breezes rustle

leaves and twigs. In

stronger gusts, whole

branches sway. Strong,

powerful winds may

snap or uproot trees

and cause widespread

damage. A wind that

blows most often in a

particular area is called

a prevailing wind.

In each cell,

warm air rises

from below

then cool air

blows in to

take its place

Winds blow around

the globe in six main

circular movements,

called cells

Winds

MONSOONS

Polar

easterlies

Polar

easterlies

Trade

winds

Trade

winds

Earth’s

spin

Westerlies

Westerlies

Equator

FIND OUT MORE. Asia 260–261 • Atmosphere 49 • Rain 52–53 • Storms 54

winds