Download Air Pressure and Wind

Air Pressure and Wind
Chapter 10 Lesson 6
Height and Air Pressure
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Air Pressure depends on the weight of the
molecules pressing down on a given area.
Molecules are denser (or compacted) at sea
level, rather than higher in the atmosphere.
You could take the same amount of air from sea
level and from up in the atmosphere, and the air
that is at sea level would be more dense than
the air taken from the atmosphere.
Air Pressure and Temperature
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When air is heated its molecules begin to
speed up and spread out.
The same amount of air will weigh less
and the pressure will be decreased.
Water Vapor and Air Pressure
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Air is composed of nitrogen, oxygen, and
other gases.
Water Vapor (which is not a gas, but tiny
particles of water), weigh less than the
gasses in the air.
Moist air exerts less pressure than dry air.
What makes wind and How does it
Blow!
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Think of play dough. When you squish it under
your flat palm, the play dough moves to cracks
between your fingers, or even tries to squish out
from under your hand. Wind is the same
concept.
Dense Air always tries to find Areas of Less
Dense Air. This horizontal movement is called
Wind.
Air that moves upward is called an updraft.
Air that moves downward is called a downdraft.
What is a Convection Cell
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A convection cell is a part of the
atmosphere where air moves in a circular
pattern because of unequal heating and
cooling.
Isolation (or the suns rays play an
important role when it comes to making
wind. WHY?)
What Makes a Convection Cell?
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The Sun’s rays hit an area, and they transfer
energy to the air, heating it up.
The warmer the air the less dense it becomes.
The warm air rises, creating an updraft.
While the warm air rises, denser air (cooler air
takes its place)
The warm air after it is in the atmosphere starts
to cool off and sink.
This circular pattern is called a convection cell
and also describes how winds blow.
What is a Sea Breeze
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Happens when…Its DAY TIME.
Air over Land heats up faster than Air over
water.
The warm air rises and the denser air over
the water moves horizontally to the land.
A wind that blows from Ocean to
Land is called a Sea Breeze.
Sea and Land Breezes
What is a Land Breeze
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Happens when… It is NIGHT TIME.
The Air over the land cools more rapidly
than the air over the water.
Hot Air over the water rises and cooler air
from the land moves horizontally to the
sea.
A Land Breeze is when Air moves
from Land to Sea.
Valley Breezes
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During the Day, the sun shines on an area
of higher elevation. (such as a Mountain)
The air on the slope of the mountain will
heat up faster than the air at the bottom
of the valley floor.
The cooler air of the valley flows up the
side of the mountain to replace the
warming air.
This is called a Valley Breeze.
Mountain Breeze
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A Mountain Breeze happens when it is Night
Time.
The valley air is warmer than the side of the
Mountain. (this happens because of a rapid cool
down)
The valley air will rise, and be replaced with a
breeze coming from the top of the mountain.
Air moving down the slope of a Mountain is
called a Mountain Breeze.
What is the Coriolis Effect?
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The Coriolis Effect is the curving of the
wind due to the rotation of the Earth.
The Earth Spins to the right, and so the
air in the Northern Hemisphere curves to
the right, while the wind in the Southern
Hemisphere curves to the Left.
The Coriolis Effect also affects the Oceans
Currents.
Coriolis Effect
Side Note (this will help in
upcoming lessons)
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In the Northern Hemisphere wind always
blows counterclockwise around the center
of a low pressure system.
The wind will blow clockwise around the
center of a high pressure system.
How are Global Wind Patterns
Produced?
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Year round the Equator is heated by strong
sunlight. This causes the air in this region to be
warm and moist. It creates a zone of Low Air
Pressure around the word, that we know as the
Equator.
As the air warms it becomes less dense and
rises. As it rises it hits the top of the
Troposphere and begins to spread out to the
North and South and slowly starts to cool down
and sink to the surface of the Earth.
Global Wind Patterns
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At about 30 degrees North and South of the
Equator, the warm air that has been in the
atmosphere, is now starting to sink and fall
down wards. This will create an area of High Air
Pressure from 30 degrees North through the
Equator to 30 degrees South.
Because, the High Air Pressure is seeking out
the Low Air Pressure, a belt of wind is set into
motion. We call these winds the Trade Winds.
Global Wind Patterns
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The Poles have very little sunlight and very cold
air. Cold air can not hold a lot of water vapor,
and because cold air can hold little water vapor,
the air at the poles will be very dry air.
This dry cold air, gives the poles a high air
pressure.
The winds that can be found between the 90
and 60 degree mark are called the Polar
Easterlies.
Global Winds
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Between the 60 and 30 degrees lines on a
globe, an area of Low air pressure exists.
This area also has winds known as the
Prevailing Westerly Winds.
The United States can be found in this
zone.
Isobars
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Isobars are lines that connect areas of
equal air pressure, on a map.
Isobars help us to see patterns of air
pressure.
Air Pressure Systems
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High Air Pressure Systems have winds that
blow from the center of the system to the
outside of the system, in a counter
clockwise rotation.
Low Air Pressure Systems have winds that
blow from the outside to the inside of the
system. Be Careful because in the center
of a low air pressure system you can find
a high air pressure system.
Isobars.
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When you look at a map
that has Isobars on it,
you will notice that some
lines are closer together
than others. Lines that
are close together mean
that the winds are really
strong. However; the
further away the lines are
from each other the
weaker the winds.