Air Pressure and WindAir Pressure and Wind

Chapter 10 Lesson 6Chapter 10 Lesson 6

Height and Air PressureHeight and Air Pressure

Air Pressure depends on the weight of the Air Pressure depends on the weight of the molecules pressing down on a given area.molecules pressing down on a given area.

Molecules are denser (or compacted) at Molecules are denser (or compacted) at sea level, rather than higher in the sea level, rather than higher in the atmosphere. atmosphere.

You could take the same amount of air You could take the same amount of air from sea level and from up in the from sea level and from up in the atmosphere, and the air that is at sea level atmosphere, and the air that is at sea level would be more dense than the air taken would be more dense than the air taken from the atmosphere.from the atmosphere.

Air Pressure and TemperatureAir Pressure and Temperature

When air is heated its molecules When air is heated its molecules begin to speed up and spread out.begin to speed up and spread out.

The same amount of air will weigh The same amount of air will weigh less and the pressure will be less and the pressure will be decreased.decreased.

Water Vapor and Air PressureWater Vapor and Air Pressure

Air is composed of nitrogen, oxygen, Air is composed of nitrogen, oxygen, and other gases.and other gases.

Water Vapor (which is not a gas, but Water Vapor (which is not a gas, but tiny particles of water), weigh less tiny particles of water), weigh less than the gasses in the air.than the gasses in the air.

Moist air exerts less pressure than Moist air exerts less pressure than dry air.dry air.

What makes wind and How does it What makes wind and How does it Blow!Blow!

Think of play dough. When you squish it Think of play dough. When you squish it under your flat palm, the play dough under your flat palm, the play dough moves to cracks between your fingers, or moves to cracks between your fingers, or even tries to squish out from under your even tries to squish out from under your hand. Wind is the same concept.hand. Wind is the same concept.

Dense Air always tries to find Areas of Less Dense Air always tries to find Areas of Less Dense Air. This horizontal movement is Dense Air. This horizontal movement is called Wind.called Wind.

Air that moves upward is called an updraft.Air that moves upward is called an updraft. Air that moves downward is called a Air that moves downward is called a

downdraft.downdraft.

What is a Convection CellWhat is a Convection Cell

A convection cell is a part of the A convection cell is a part of the atmosphere where air moves in a atmosphere where air moves in a circular pattern because of unequal circular pattern because of unequal heating and cooling.heating and cooling.

Isolation (or the suns rays play an Isolation (or the suns rays play an important role when it comes to important role when it comes to making wind. WHY?)making wind. WHY?)

What Makes a Convection Cell?What Makes a Convection Cell?

The Sun’s rays hit an area, and they The Sun’s rays hit an area, and they transfer energy to the air, heating it up.transfer energy to the air, heating it up.

The warmer the air the less dense it The warmer the air the less dense it becomes. becomes.

The warm air rises, creating an updraft.The warm air rises, creating an updraft. While the warm air rises, denser air (cooler While the warm air rises, denser air (cooler

air takes its place)air takes its place) The warm air after it is in the atmosphere The warm air after it is in the atmosphere

starts to cool off and sink.starts to cool off and sink. This circular pattern is called a convection This circular pattern is called a convection

cell and also describes how winds blow.cell and also describes how winds blow.

What is a Sea BreezeWhat is a Sea Breeze

Happens when…Its Happens when…Its DAY TIMEDAY TIME.. Air over Land heats up faster than Air Air over Land heats up faster than Air

over water.over water. The warm air rises and the denser air The warm air rises and the denser air

over the water moves horizontally to over the water moves horizontally to the land.the land.

A wind that blows from Ocean to A wind that blows from Ocean to Land is called a Sea Breeze.Land is called a Sea Breeze.

Sea and Land BreezesSea and Land Breezes

What is a Land BreezeWhat is a Land Breeze

Happens when… It is Happens when… It is NIGHT TIMENIGHT TIME.. The Air over the land cools more The Air over the land cools more

rapidly than the air over the water.rapidly than the air over the water. Hot Air over the water rises and Hot Air over the water rises and

cooler air from the land moves cooler air from the land moves horizontally to the sea.horizontally to the sea.

A Land Breeze is when Air moves A Land Breeze is when Air moves from Land to Sea.from Land to Sea.

Valley BreezesValley Breezes

During the Day, the sun shines on an During the Day, the sun shines on an area of higher elevation. (such as a area of higher elevation. (such as a Mountain)Mountain)

The air on the slope of the mountain The air on the slope of the mountain will heat up faster than the air at the will heat up faster than the air at the bottom of the valley floor.bottom of the valley floor.

The cooler air of the valley flows up The cooler air of the valley flows up the side of the mountain to replace the side of the mountain to replace the warming air.the warming air.

This is called a Valley Breeze.This is called a Valley Breeze.

Mountain BreezeMountain Breeze

A Mountain Breeze happens when it is A Mountain Breeze happens when it is Night Time.Night Time.

The valley air is warmer than the side of The valley air is warmer than the side of the Mountain. (this happens because of a the Mountain. (this happens because of a rapid cool down) rapid cool down)

The valley air will rise, and be replaced The valley air will rise, and be replaced with a breeze coming from the top of the with a breeze coming from the top of the mountain.mountain.

Air moving down the slope of a Mountain is Air moving down the slope of a Mountain is called a Mountain Breeze.called a Mountain Breeze.

What is the Coriolis Effect?What is the Coriolis Effect?

The Coriolis Effect is the curving of the The Coriolis Effect is the curving of the wind due to the rotation of the Earth.wind due to the rotation of the Earth.

The Earth Spins to the right, and so the The Earth Spins to the right, and so the air in the Northern Hemisphere curves air in the Northern Hemisphere curves to the right, while the wind in the to the right, while the wind in the Southern Hemisphere curves to the Left.Southern Hemisphere curves to the Left.

The Coriolis Effect also affects the The Coriolis Effect also affects the Oceans Currents.Oceans Currents.

Coriolis EffectCoriolis Effect

Side Note (this will help in Side Note (this will help in upcoming lessons)upcoming lessons)

In the Northern Hemisphere wind In the Northern Hemisphere wind always blows counterclockwise always blows counterclockwise around the center of a low pressure around the center of a low pressure system.system.

The wind will blow clockwise around The wind will blow clockwise around the center of a high pressure system.the center of a high pressure system.

How are Global Wind Patterns How are Global Wind Patterns Produced?Produced?

Year round the Equator is heated by strong Year round the Equator is heated by strong sunlight. This causes the air in this region to sunlight. This causes the air in this region to be warm and moist. It creates a zone of be warm and moist. It creates a zone of Low Air Pressure around the word, that we Low Air Pressure around the word, that we know as the Equator.know as the Equator.

As the air warms it becomes less dense and As the air warms it becomes less dense and rises. As it rises it hits the top of the rises. As it rises it hits the top of the Troposphere and begins to spread out to the Troposphere and begins to spread out to the North and South and slowly starts to cool North and South and slowly starts to cool down and sink to the surface of the Earth.down and sink to the surface of the Earth.

Global Wind PatternsGlobal Wind Patterns

At about 30 degrees North and South of At about 30 degrees North and South of the Equator, the warm air that has been in the Equator, the warm air that has been in the atmosphere, is now starting to sink and the atmosphere, is now starting to sink and fall down wards. This will create an area of fall down wards. This will create an area of High Air Pressure from 30 degrees North High Air Pressure from 30 degrees North through the Equator to 30 degrees South.through the Equator to 30 degrees South.

Because, the High Air Pressure is seeking Because, the High Air Pressure is seeking out the Low Air Pressure, a belt of wind is out the Low Air Pressure, a belt of wind is set into motion. We call these winds the set into motion. We call these winds the Trade Winds.Trade Winds.

Global Wind PatternsGlobal Wind Patterns

The Poles have very little sunlight and The Poles have very little sunlight and very cold air. Cold air can not hold a lot of very cold air. Cold air can not hold a lot of water vapor, and because cold air can hold water vapor, and because cold air can hold little water vapor, the air at the poles will little water vapor, the air at the poles will be very dry air.be very dry air.

This dry cold air, gives the poles a high air This dry cold air, gives the poles a high air pressure.pressure.

The winds that can be found between the The winds that can be found between the 90 and 60 degree mark are called the 90 and 60 degree mark are called the Polar Easterlies.Polar Easterlies.

Global WindsGlobal Winds

Between the 60 and 30 degrees lines Between the 60 and 30 degrees lines on a globe, an area of Low air on a globe, an area of Low air pressure exists. pressure exists.

This area also has winds known as This area also has winds known as the Prevailing Westerly Winds.the Prevailing Westerly Winds.

The United States can be found in The United States can be found in this zone.this zone.

IsobarsIsobars

Isobars are lines that connect areas Isobars are lines that connect areas of equal air pressure, on a map.of equal air pressure, on a map.

Isobars help us to see patterns of air Isobars help us to see patterns of air pressure.pressure.

Air Pressure SystemsAir Pressure Systems

High Air Pressure Systems have winds High Air Pressure Systems have winds that blow from the center of the that blow from the center of the system to the outside of the system, system to the outside of the system, in a counter clockwise rotation.in a counter clockwise rotation.

Low Air Pressure Systems have winds Low Air Pressure Systems have winds that blow from the outside to the that blow from the outside to the inside of the system. Be Careful inside of the system. Be Careful because in the center of a low air because in the center of a low air pressure system you can find a high pressure system you can find a high air pressure system.air pressure system.

Isobars.Isobars.

When you look at a When you look at a map that has Isobars map that has Isobars on it, you will notice on it, you will notice that some lines are that some lines are closer together than closer together than others. Lines that are others. Lines that are close together mean close together mean that the winds are that the winds are really strong. However; really strong. However; the further away the the further away the lines are from each lines are from each other the weaker the other the weaker the winds.winds.