Transcript Winds

Winds
Measuring wind
 Winds are described by their
direction and speed.
 Speed of wind is measured by an
anemometer.( Has three cups
mounted at the end of spokes that
spin on an axle. The spinning of
the cups is measured by a
speedometer
 The direction measured by a
weather vane. The name of the
wind tells you the direction it is
coming from. Ex. South winds
blow from the south to the North
What causes the winds?
 Air is a fluid, so it can move easily from
place to place.
 Fluids move areas of from high pressure
to low pressure
 All winds are caused by difference in air
pressure!!!!
 Turn to your partner and discuss the
density of low pressure, compared to the
density of a high pressure
Local winds
 This wind occurs when there is a
large body of water near by.
 During the day: There might not
be wind inland, but there may be a
wind blowing from the water
towards the beach or large body
of water.
 They are caused by unequal
heating of the Earth’s surface in a
small area.
 Local winds blow when there is no
other winds blowing from far away.
 It takes more energy to heat water
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than the land. So land heats
quicker than water.
The water is cooler, so it’s density
is greater than the heat molecules
on land.
The higher pressure above the
water moves underneath the hot
lower pressure and pushes the air
up causing a breeze.
This is called a sea or lake breeze
At night the opposite happens, this
is called a land breeze
Turn to your partner and draw
what causes sea breezes during
the day on the white boards.
Monsoons
 Similar to sea breezes, but occurs
over wider areas.
 In South and Southeast Asia
 The land gets hotter than the
ocean, and this heating occurs all
summer. In the winter the land
cools faster than the ocean, so the
higher pressure above the land,
moves under the higher pressure
above the ocean.
 This causes humid heat to rise
into the air inside the water vapor.
As it cools condensation takes
place and then heavy precipitation
occurs, which is needed for crops
Global Winds
 Caused by unequal heating of
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the Earth’s surface.
The direct rays near the
equator are more intense the
light hitting the poles
The pressure at the poles is
greater than at the equator.
This uneven heating causes
giant convection currents.
The High pressure moves
down towards the lower
pressure at the equator, this
moves under the low pressure
at the equator pushing the air
at the equator up to the poles.
Coriolis Effect
 If the Earth didn’t spin the
global wind would blow in
a straight line from poles
to equator
 The Earth spins from east
to west, making these
winds curve counterclockwise
 In Northern Hemisphere
the global winds turn right
 In Southern Hemisphere
the winds turn to the left
Other types of Winds
 Doldrums: Near the equator.
 The sun heats strongly, warm air rises and
creates low pressure, when cool air comes
in (Higher pressure) It gets warmed to
quickly to push the low pressure anywhere
(heated air)
Is sailing a sail boat in this region wise?
Explain to your partner.
Horse Latitudes
 30 degrees north and south of the equator
the air stops moving towards the poles
and sinks, so another area of very little
wind forms.
 Hundreds of years ago sailors, ran out of
food and water for their horses that they
brought with them, and they had to throw
the horses overboard.
Trade Winds
 When cold air over the horse latitudes sinks, it produces
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a region of high pressure
This high pressure causes surfaces winds to blow
towards and away from the equator
The winds toward the equator are turned west by the
coriolis effect
These winds are constant . In the Northern Hemisphere
the blow from 30 degrees latitude towards the equator
from the northeast.
In the Southern Hemisphere the blow from 30 degrees
latitude towards the equator from the southeast.
Westerlies
 In the middle latitudes, winds that blow
towards the poles are turned toward the
East because of the Coriolis effect
 Called westerlies because they blow from
west to east
 Blow from the southwest between 30 and
60 degrees latitude at both hemispheres
 They play an important part in the weather
in the United States
Jet Streams
 10 km above the Earth’s surface are high
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speed winds called the jet stream.
They are hundreds of km. wide, but only a
few km deep
They blow from west to east
At speeds of 200-400 km/h
Pilots fly east in the jet stream
Why might they do this?
Polar Easterlies
 Cold air near the poles sink and flows back
toward the lower latitudes
 The coriolis effect shifts these polar winds to the
west producing winds
 The Easterlies meet the westerlies at about 60
degrees in both hemispheres along the Polar
Front
 This mixing of high and low pressures has a
major effect on weather changes in the United
States.