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Winds
- What is Wind?
- How does it blow?
- Upper Winds ~ Jet Stream
- Surface Winds ~ Trade Winds
- Local Winds ~ Sea breezes and land breezes
- How to measure Wind?
- The Coriolis Effect
- The Uses of Wind
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| What
is Wind? |
 What
is Wind?
Wind
is moving air. The Sun heats up some parts of the Earth more than
others and the wind spreads this heat more evenly around the world.
The map shows the main world and local winds.
Local Winds Winds affect
the weather and are given special names in many parts of the world.
| Brickfielder
|
Very
hot north-east summer wind that blows dust and sand across Australia. |
| Chincook
|
Warm,
dry wind of the Rocky Mountains, USA. Welcomed by cattlemen
because it can remove snow cover very quickly. Named after a
local Indian tribe. |
| Fohn
|
Warm,
dry European wind that flows down the side of mountains. |
| Haboob
|
The
Arabic name for a violent wind which raises sandstorms, especially
in North Africa. |
| Levanter
|
Pleasant,
moist east wind that brings mild weather to the Mediterranean. |
| Mistral
|
Violent,
dry, cold, north-west wind that blows along the coasts of Spain
and France. |
| Sciroco
|
Hot,
dry South wind that blows across North Africa from the Sahara.
Becomes very hot and sticky as it reaches the sea. |
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| How
does it blow? |
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How
does it blow? 
Air moves
because of differences in pressure around the world. It blows from
a high- pressure area to a low- pressure area.
Let's
focus on a few types of winds. There are 3 major types of winds:
upper winds, surface winds and local winds.
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| Upper
Winds |
|
1.
Upper Winds
Upper
winds can be found at least 10 km above the ground, such as jet
streams.
Jet
Streams
Jet streams
are very strong winds blowing about 10km above the Earth. They can
be up to 4, 000 km long but no more than 500km wide. They were not
discovered until World War II when pilots found their air speed
reduced when they were flying against the jet stream.
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| Surface
Winds |
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2.
Surface Winds
Surface
winds refer to the winds which are blowing near to the Earth's surface,
usually you can find it several km above the ground, such as trade
winds.
Trade
Winds
The trade
winds are steady winds flowing towards the Equator. In the 18th
century sailing ships used them as guides for crossing the Atlantic
Ocean. Columbus might never have discovered America in 1492 without
the trade winds' help.
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| Local
Winds |
|
3.
Local Winds
Local
winds occur in a narrow region, e.g. land and sea breezes, which
are found along the coastal areas.
Sea
Breezes and Land Breezes
On a
hot, sunny day the land heats up more quickly than the sea. Because
of this air rises over the land and cool sea breezes rush in to
replace it. This is called Sea Breeze.
By evening
sea breezes can reach 200 km inland. At night land cools down more
quickly than the sea so the breeze blows out from land to sea.
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How
to measure Wind? |
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How
to measure Wind? (diagram)
The two
most important things about the wind are its speed and direction
in which it is blowing. We use a weather vane or a windsock (a kind
of long cloth tube through which the wind is funnelled) to see wind
direction. It is expressed in compass points. Wind speed is measured
by the Beaufort Scale, windsocks or by special scientific instruments
called anemometers. The unit of measurement is kilometres per hour
(km/h) or knots.
The Beaufort
Scale The Beaufort Scale was invented in 1805 by Admiral Beaufort
to estimate wind speed through observations of objects. The original
scale was for use at sea but it has been adapted for use on land.
The Beaufort Scale
| Force |
Strength |
Weather
Symbol |
km/h |
Effect |
| 0
|
Calm |
|
0-1 |
Smoke
rises vertically |
| 1
|
Light
air |
|
1-5
|
Smoke
drifts slowly |
| 2
|
Light
breeze |
|
6-11 |
Wind felt on face; leaves rustle |
| 3 |
Gentle
breeze |
|
12-19 |
Twigs
move; light flag unfurls |
| 4 |
Moderate
breeze |
|
20-29 |
Dust
and paper blown about; small branches move |
| 5 |
Fresh breeze |
|
30-39
|
Wavelets
on inland water; small trees move |
| 6 |
Strong
breeze |
|
40-50 |
Large
branches sway; umbrellas turn inside out |
| 7 |
Near
gale |
|
51-61
|
Whole
trees sway; difficult to walk against wind |
| 8 |
Gale
|
|
62-74
|
Twigs
break off trees; walking very hard |
| 9 |
Strong
gale |
|
75-87
|
Chimney
pots, roof tiles and branches blown down |
| 10 |
Storm |
|
88-101 |
Widespread
damage to buildings |
| 11 |
Violent
Storm |
|
102-117
|
Widespread
damage to buildings |
| 12 |
Hurricane
|
|
Over
119 |
Devastation |
|
 DID
You Know?
A wind that blows as fast as the fastest man can run (43kph),
is only a 'strong breeze' on the Beaufort Scale. A wind as fast as
a running cheetah (113 kph), the world fastest animal, registers as
a ' storm'. |
| The
Coriolis Effect |
|
The
Coriolis Effect
As mentioned in the previous section, wind speed and wind direction
are affected by air pressure. In addition to this, the wind direction
can be also affected by the Coriolis Effect. 
The Earth
spins on its axis, which affects the direction of the wind. In the
Northern hemisphere winds are swung to the right, and in the Southern
to the left. This is called the Coriolis Effect. This is one of
the factors affecting the wind direction.
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| The
Uses of Wind |
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The
Uses of Wind
A.
Windblown
Ship designers
are now going back to building sailing ships to take the advantage
of the wind. In August 1980, a Japanese tanker, the Shinaltoku Maru,
was launched. As well as an engine it had two square sails, controlled
by computer.
B.
Wind power 
Windmills
were once used to grind wheat to make flour. Today they are being
used to generate electricity. The windmill at Tvind, Denmark is
over 50m high with three blades, each over 5 tones. It can produce
enough electricity to light up about 120 homes.
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