Download 3 Layers of the Atmosphere

Unit 3: Atmosphere
Cheryl Lewis
Dana Desonie, Ph.D.
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AUTHORS
Cheryl Lewis
Dana Desonie, Ph.D.
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Printed: September 17, 2013
iii
Contents
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Contents
1
Importance of the Atmosphere
1
2
Pressure and Density of the Atmosphere
5
3
Layers of the Atmosphere
8
4
Electromagnetic Energy in the Atmosphere
15
5
Temperature and Heat in the Atmosphere
19
6
Heat Transfer in the Atmosphere
21
7
Heat Budget of Planet Earth
24
8
Greenhouse Effect
27
9
Circulation in the Atmosphere
30
10 Local Winds
34
11 Global Wind Belts
40
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C HAPTER
Chapter 1. Importance of the Atmosphere
1
Importance of the
Atmosphere
• Describe Earth’s atmosphere and explain the important roles it plays in sustaining life on Earth.
If Earth didn’t have an atmosphere, would it always be cold?
This is a question commonly asked by 12-year-old girls being driven to school by their mothers. "Of course," the
moms answer, "it would be extremely hot when the sun is out and bitter cold when it’s dark." Does this conversation
sound familiar?
What Is the Atmosphere?
Earth’s atmosphere is a thin blanket of gases and tiny particles — together called air. We are most aware of air when
it moves and creates wind. Earth’s atmosphere, along with the abundant liquid water at Earth’s surface, are the keys
to our planet’s unique place in the solar system. Much of what makes Earth exceptional depends on the atmosphere.
For example, all living things need some of the gases in air for life support. Without an atmosphere, Earth would
likely be just another lifeless rock.
Let’s consider some of the reasons we are lucky to have an atmosphere.
Gases Indispensable for Life on Earth
Without the atmosphere, Earth would look a lot more like the Moon. Atmospheric gases, especially carbon dioxide
(CO2 ) and oxygen (O2 ), are extremely important for living organisms. How does the atmosphere make life possible?
How does life alter the atmosphere?
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FIGURE 1.1
The composition of Earth’s atmosphere.
Photosynthesis
In photosynthesis, plants use CO2 and create O2 . Photosynthesis is responsible for nearly all of the oxygen currently
found in the atmosphere.
The chemical reaction for photosynthesis is:
6CO2 + 6H2 O + solar energy → C6 H12 O6 (sugar) + 6O2
Respiration
By creating oxygen and food, plants have made an environment that is favorable for animals. In respiration, animals
use oxygen to convert sugar into food energy they can use. Plants also go through respiration and consume some of
the sugars they produce.
The chemical reaction for respiration is:
C6 H12 O6 + 6O2 → 6CO2 + 6H2 O + useable energy
How is respiration similar to and different from photosynthesis? They are approximately the reverse of each other.
In photosynthesis, CO2 is converted to O2 and in respiration, O2 is converted to CO2 (Figure 1.2).
Crucial Part of the Water Cycle
As part of the hydrologic cycle, water spends a lot of time in the atmosphere, mostly as water vapor. The atmosphere
is an important reservoir for water.
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Chapter 1. Importance of the Atmosphere
FIGURE 1.2
Chlorophyll indicates the presence of
photosynthesizing plants as does the vegetation index.
Ozone Makes Life on Earth Possible
Ozone is a molecule composed of three oxygen atoms, (O3 ). Ozone in the upper atmosphere absorbs high-energy
ultraviolet (UV) radiation coming from the Sun. This protects living things on Earth’s surface from the Sun’s most
harmful rays. Without ozone for protection, only the simplest life forms would be able to live on Earth. The highest
concentration of ozone is in the ozone layer in the lower stratosphere.
Keeps Earth’s Temperature Moderate
Along with the oceans, the atmosphere keeps Earth’s temperatures within an acceptable range. Without an atmosphere, Earth’s temperatures would be frigid at night and scorching during the day. If the 12-year-old in the scenario
above asked why, she would find out. Greenhouse gases trap heat in the atmosphere. Important greenhouse gases
include carbon dioxide, methane, water vapor, and ozone.
Provides the Substance for Waves to Travel Through
The atmosphere is made of gases that take up space and transmit energy. Sound waves are among the types of energy
that travel though the atmosphere. Without an atmosphere, we could not hear a single sound. Earth would be as
silent as outer space (explosions in movies about space should be silent). Of course, no insect, bird, or airplane
would be able to fly, because there would be no atmosphere to hold it up.
Summary
• The atmosphere is made of gases that are essential for photosynthesis and respiration, among other life
activities.
• The atmosphere is a crucial part of the water cycle. It is an important reservoir for water and the source of
precipitation.
• The atmosphere moderates Earth’s temperature because greenhouse gases absorb heat.
Vocabulary
• Atmosphere: thin layer of gases that surrounds the Earth
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• Ozone: molecule composed of three oxygen atoms, (O3 ). Ozone in the upper atmosphere absorbs highenergy ultraviolet (UV) radiation coming from the Sun, protecting living things on Earth’s surface from the
Sun’s most harmful rays.
Practice
Use these resources to answer the questions that follow.
http://www.hippocampus.org/Earth%20Science → Environmental Science → Search: Photosynthesis
1. How does photosynthesis occur?
2. What does photosynthesis create?
http://dsc.discovery.com/videos/assignment-discovery-shorts-06-07-07-08-cellular-respiration.html
MEDIA
Click image to the left for more content.
3. What is cellular respiration?
4. Why does glycolysis produce?
5. What are the 3 steps of cellular respiration?
Review
1. What gases are used and expelled by photosynthesis and respiration?
2. Where is the largest concentration of ozone and what value does it have?
3. How does the atmosphere keep Earth’s temperature moderate?
References
1. Mysid. . Public Domain
2. Provided by the SeaWiFS Project, NASA/Goddard Space Flight Center and ORBIMAGE. . Public Domain
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C HAPTER
Chapter 2. Pressure and Density of the Atmosphere
2
Pressure and Density of the
Atmosphere
• Define air density and air pressure and explain how they change with increasing altitude.
Have your ears ever popped?
If your ears have ever "popped," you have experienced a change in air pressure. Ears "pop" because the air pressure
is different on the inside and the outside.
Pressure and Density
The atmosphere has different properties at different elevations above sea level, or altitudes.
Density
The air density (the number of molecules in a given volume) decreases with increasing altitude. This is why people
who climb tall mountains, such as Mt. Everest, have to set up camp at different elevations to let their bodies get used
to the decreased air density (Figure 2.1).
Why does air density decrease with altitude? Gravity pulls the gas molecules towards Earth’s center. The pull of
gravity is stronger closer to the center, at sea level. Air is denser at sea level, where the gravitational pull is greater.
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Pressure
Pressure is a force pushing on an area or surface. Gases at sea level are also compressed by the weight of the
atmosphere above them. The force of the air weighing down over a unit of area is known as its atmospheric pressure,
or air pressure. Why are we not crushed? The molecules inside our bodies are pushing outward to compensate. Air
pressure is felt from all directions, not just from above.
FIGURE 2.1
This bottle was closed at an altitude of 2,000 meters where air pressure is lower. When it was brought down to
sea level, the higher air pressure caused the bottle to collapse.
At higher altitudes the atmospheric pressure is lower and the air is less dense than at lower altitudes. That’s what
makes your ears pop when you change altitude. Gas molecules are found inside and outside your ears. When you
change altitude quickly, like when an airplane is descending, your inner ear keeps the density of molecules at the
original altitude. Eventually the air molecules inside your ear suddenly move through a small tube in your ear to
equalize the pressure. This sudden rush of air is felt as a popping sensation.
A barometer measures air pressure.There are two kinds of barometers: mercury barometers and aneroid barometers.
Summary
• Air density and pressure decrease with increasing altitude.
• Ears pop as air pressure inside and outside the ear equalizes.
• Gravity pulls more air molecules toward the center of the planet.
Vocabulary
• Air pressure: force of the air weighing down over a unit of area
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Chapter 2. Pressure and Density of the Atmosphere
Practice
Use this resource to answer the questions that follow.
http://www.youtube.com/watch?v=7_yf-iRf8Vc
MEDIA
Click image to the left for more content.
1. What is pressure?
2. What does air have?
3. Where does the atmosphere end?
4. What is air pressure?
5. What is the air pressure in Key West, Florida?
6. Explain the relationship between air pressure and altitude.
Review
1. Why does air density decrease with altitude?
2. Temperature also decreases with altitude. How does that relate to the change in air density?
3. Why are we not crushed by the weight of the atmosphere on our shoulders?
References
1. David Monniaux. . CC-BY-SA 2.0 France
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C HAPTER
3
Layers of the Atmosphere
Lesson Objectives
•
•
•
•
•
•
Describe how the temperature of the atmosphere changes with altitude.
Outline the properties of the troposphere.
Explain the role of the ozone layer in the stratosphere.
Describe conditions in the mesosphere.
Explain how the sun affects the thermosphere.
Identify the exosphere.
Vocabulary
•
•
•
•
•
•
•
•
•
exosphere
ionosphere
mesosphere
ozone
stratosphere
temperature inversion
thermosphere
troposphere
altitude
Introduction
Earth’s atmosphere is divided into five major layers. The layers are based on temperature and are at different heights
in the atmosphere, referred to as altitude.
Temperature of the Atmosphere
Air temperature changes as altitude increases. In some layers of the atmosphere, the temperature decreases. In other
layers, it increases. You can see this in Figure 3.1. Refer to this figure as you read about the layers below.
Troposphere
The troposphere is the lowest layer of the atmosphere. In it, temperature decreases with altitude. The troposphere
gets some of its heat directly from the sun. Most, however, comes from Earth’s surface. The surface is heated by
the sun and some of that heat radiates back into the air. This makes the temperature higher near the surface than at
higher altitudes.
Properties of the Troposphere
Look at the troposphere in Figure 3.1. This is the shortest layer of the atmosphere. It rises to only about 12 kilometers
(7 miles) above the surface. Even so, this layer holds 75 percent of all the gas molecules in the atmosphere. That’s
because the air is densest in this layer.
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Chapter 3. Layers of the Atmosphere
FIGURE 3.1
How does air temperature change in the
layer closest to Earth?
Mixing of Air
Air in the troposphere is warmer closer to Earth’s surface. Warm air is less dense than cool air, so it rises higher in
the troposphere. This starts a convection cell. Convection mixes the air in the troposphere. Rising air is also a main
cause of weather. All of Earth’s weather takes place in the troposphere.
Temperature Inversion
Sometimes air doesn’t mix in the troposphere. This happens when air is cooler close to the ground than it is above.
The cool air is dense, so it stays near the ground. This is called a temperature inversion. An inversion can trap air
pollution near the surface. Temperature inversions are more common in the winter. Can you explain why?
Tropopause
At the top of the troposphere is a thin layer of air called the tropopause. You can see it in Figure 3.1. This layer acts
as a barrier. It prevents cool air in the troposphere from mixing with warm air in the stratosphere.
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FIGURE 3.2
Temperature Inversion and Air Pollution.
How does a temperature inversion affect
air quality?
Stratosphere
The stratosphere is the layer above the troposphere. The layer rises to about 50 kilometers (31 miles) above the
surface.
Temperature in the Stratosphere
Air temperature in the stratosphere layer increases with altitude. Why? The stratosphere gets most of its heat from
the sun. Therefore, it’s warmer closer to the sun. The air at the bottom of the stratosphere is cold. The cold air is
dense, so it doesn’t rise. As a result, there is little mixing of air in this layer.
The Ozone Layer
The stratosphere contains a layer of ozone gas. Ozone consists of three oxygen atoms (O3 ). The ozone layer absorbs
high-energy UV radiation. As you can see in Figure 3.3, UV radiation splits the ozone molecule. The split creates
an oxygen molecule (O2 ) and an oxygen atom (O). This split releases heat that warms the stratosphere. By absorbing
UV radiation, ozone also protects Earth’s surface. UV radiation would harm living things without the ozone layer.
Stratopause
At the top of the stratosphere is a thin layer called the stratopause. It acts as a boundary between the stratosphere
and the mesosphere.
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Chapter 3. Layers of the Atmosphere
FIGURE 3.3
How does the ozone layer protect Earth’s
surface from UV light?
Mesosphere
The mesosphere is the layer above the stratosphere. It rises to about 85 kilometers (53 miles) above the surface.
Temperature decreases with altitude in this layer.
Temperature in the Mesosphere
There are very few gas molecules in the mesosphere. This means that there is little matter to absorb the sun’s rays
and heat the air. Most of the heat that enters the mesosphere comes from the stratosphere below. That’s why the
mesosphere is warmest at the bottom.
Meteors in the Mesosphere
Did you ever see a meteor shower, like the one in Figure 3.4? Meteors burn as they fall through the mesosphere.
The space rocks experience friction with the gas molecules. The friction makes the meteors get very hot. Many
meteors burn up completely in the mesosphere.
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FIGURE 3.4
Friction with gas molecules causes meteors to burn up in the mesosphere.
Mesopause
At the top of the mesosphere is the mesopause. Temperatures here are colder than anywhere else in the atmosphere.
They are as low as -100° C (-212° F)! Nowhere on Earth’s surface is that cold.
Thermosphere
The thermosphere is the layer above the mesosphere. It rises to 600 kilometers (372 miles) above the surface. The
International Space Station orbits Earth in this layer as in Figure 3.5.
FIGURE 3.5
The International Space Station orbits in
the thermosphere.
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Chapter 3. Layers of the Atmosphere
Temperature in the Thermosphere
Temperature increases with altitude in the thermosphere. Surprisingly, it may be higher than 1000° C (1800° F) near
the top of this layer! The sun’s energy there is very strong. The molecules absorb the sun’s energy and are heated
up. But there are so very few gas molecules, that the air still feels very cold. Molecules in the thermosphere gain or
lose electrons. They then become charged particles called ions.
Northern and Southern Lights
Have you ever seen a brilliant light show in the night sky? Sometimes the ions in the thermosphere glow at night.
Storms on the sun energize the ions and make them light up. In the Northern Hemisphere, the lights are called the
northern lights, or aurora borealis. In the Southern Hemisphere, they are called southern lights, or aurora australis.
FIGURE 3.6
Glowing ions in the thermosphere light up
the night sky.
Exosphere
The exosphere is the outer layer of the thermosphere. This is the top of the atmosphere. The exosphere has no real
upper limit; it just gradually merges with outer space. Gas molecules are very far apart in this layer, but they are
really hot. Earth’s gravity is so weak in the exosphere that gas molecules sometimes just float off into space.
Lesson Summary
• Earth’s atmosphere is divided into five major layers. The layers are based on temperature.
• The troposphere is the lowest layer. Temperature decreases with altitude in this layer. All weather takes place
here.
• The stratosphere is the layer above the troposphere. Temperature increases with altitude in this layer. The
ozone layer occurs here.
• The mesosphere is the layer above the stratosphere. Temperature decreases with altitude in this layer. Meteors
burn up here.
• The thermosphere is the layer above the mesosphere. Temperature increases with altitude in this layer. The
northern and southern lights occur here.
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• The exosphere is the highest layer. Air molecules are very far apart. They may escape Earth’s gravity and
float into space.
Lesson Review Questions
Recall
1. How does temperature change in the troposphere?
2. What is a temperature inversion?
3. Why is the ozone layer in the stratosphere important to life on Earth?
4. Where does the mesosphere get its heat?
Apply Concepts
5. Think of a creative way you could model the layers of the atmosphere. Describe your model. How does it show
temperature differences between the layers?
Think Critically
6. How is a temperature inversion like the temperatures of the stratosphere and troposphere?
7. Explain why air mixes in the troposphere but not in the stratosphere.
8. Why is there a hole in the ozone layer? What do you think the consequences of that hole are?
Points to Consider
Energy from the sun is responsible for winds that blow in the troposphere.
• What is wind?
• How does energy cause winds to blow?
References
1. Courtesy of JetStream/National Weather Service/National Oceanic and Atmospheric Administration. http://w
ww.srh.noaa.gov/jetstream//atmos/atmprofile.htm. Public Domain
2. Courtesy of National Weather Service/National Oceanic and Atmospheric Administration. http://www.wrh.n
oaa.gov/slc/climate/TemperatureInversions.php. Public Domain
3. Airplane image copyright Stasys Eidiejus, 2010; buildings image copyright wibowo, 2010; composite created
by CK-12 Foundation. http://www.shutterstock.com/. Airplane and buildings images used under licenses from
Shutterstock.com
4. Image copyright Shalygin, 2010. http://www.shutterstock.com/. Used under license from Shutterstock.com
5. Courtesy of NASA/Crew of STS-132. http://en.wikipedia.org/wiki/File:International_Space_Station_after_
undocking_of_STS-132.jpg. Public Domain
6. Varjisakka. http://en.wikipedia.org/wiki/File:Northern_Lights_02.jpg. CC-BY-SA 3.0
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C HAPTER
Chapter 4. Electromagnetic Energy in the Atmosphere
4
Electromagnetic Energy in
the Atmosphere
• Identify and define types of electromagnetic radiation.
Does cell phone use cause brain tumors?
Many studies have been done to see if the radio frequency radiation emitted by cell phones causes brain tumors. As
yet the results have mostly shown no link, although one study seemed to show some connection. The largest amount
of radiation comes when the phone first connects to a new cell phone tower, so avoid talking while driving — which
is good for other reasons as well — or when the signal is poor and the phone must emit more radiation for it to work.
There is a link between having a cell phone in your pocket and a decrease in bone density in the pelvis. What can
cause these problems? What is electromagnetic radiation?
Energy
Energy travels through space or material. This is obvious when you stand near a fire and feel its warmth or when
you pick up the handle of a metal pot even though the handle is not sitting directly on the hot stove. Invisible energy
waves can travel through air, glass, and even the vacuum of outer space. These waves have electrical and magnetic
properties, so they are called electromagnetic waves. The transfer of energy from one object to another through
electromagnetic waves is known as radiation.
Different wavelengths of energy create different types of electromagnetic waves (Figure 4.1).
• The wavelengths humans can see are known as visible light. When viewed together, all of the wavelengths of
visible light appear white. But a prism or water droplets can break the white light into different wavelengths
so that separate colors appear (Figure 4.2). What objects can you think of that radiate visible light? Two
include the Sun and a light bulb.
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FIGURE 4.1
The electromagnetic spectrum; short wavelengths are the fastest with the
highest energy.
FIGURE 4.2
A prism breaks apart white light.
• The longest wavelengths of visible light appear red. Infrared wavelengths are longer than visible red. Snakes
can see infrared energy. We feel infrared energy as heat.
• Wavelengths that are shorter than violet are called ultraviolet.
Can you think of some objects that appear to radiate visible light, but actually do not? The Moon and the planets do
not emit light of their own; they reflect the light of the Sun. Reflection is when light (or another wave) bounces back
from a surface. Albedo is a measure of how well a surface reflects light. A surface with high albedo reflects a large
percentage of light. A snow field has high albedo.
One important fact to remember is that energy cannot be created or destroyed — it can only be changed from one
form to another. This is such a fundamental fact of nature that it is a law: the law of conservation of energy.
In photosynthesis, for example, plants convert solar energy into chemical energy that they can use. They do not
create new energy. When energy is transformed, some nearly always becomes heat. Heat transfers between materials
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Chapter 4. Electromagnetic Energy in the Atmosphere
easily, from warmer objects to cooler ones. If no more heat is added, eventually all of a material will reach the same
temperature.
Summary
• Energy travels in waves with electrical and magnetic properties and so is called electromagnetic radiation.
• The wavelengths of visible light vary from long wavelength red to short wavelength violet. Infrared and
ultraviolet wavelengths continue outward at longer and shorter wavelengths.
• The law of conservation of energy states that energy cannot be created or destroyed, it can only change forms.
Vocabulary:
• Electromagnetic waves: waves that transfer electric and maganetic energy
• Visible light: Includes all the colors you see in a rainbow. Different colors have different wavelengths
• UV radiation: Electromagnetic waves with wavelengths that are shorter than visible light but longer than
x-rays
• Infrared radiation: Electromagentic waves with wavelengths that are longer than visible light but shorter
than microwaves
Practice
Use these resources to answer the questions that follow.
http://www.youtube.com/watch?v=kfS5Qn0wn2o
MEDIA
Click image to the left for more content.
1. What is the electromagnetic spectrum?
2. What is the visible spectrum?
3. Why is the visible spectrum important?
4. What pattern is unique to hydrogen?
http://www.youtube.com/watch?v=QgzggbEQ2MY
MEDIA
Click image to the left for more content.
5. What is albedo?
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6. How is albedo expressed?
7. What is the albedo of snow?
8. How is the Earth’s albedo determined?
9. What does MODIS do?
10. What is the Earth’s average temperature?
11. What happens when the rain forests are cut down?
12. What is the average albedo of the Earth?
Review
1. How is the light from the Sun different from the light from the Moon?
2. How does the energy that comes off a surface with high albedo differ from the energy that comes off a surface
with low albedo?
3. How does a child kicking a soccer ball illustrate the law of conservation of energy?
References
1. Penubag. . CC-BY-SA 2.5
2. Spigget. . CC-BY-SA 3.0
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C HAPTER
Chapter 5. Temperature and Heat in the Atmosphere
5
Temperature and Heat in the
Atmosphere
• Explain the relationship between temperature and heat.
A candle flame or a bathtub full of hot water: which has higher heat and which has the higher temperature?
The flame has higher temperature, but less heat because the hot region is very small. The bathtub has lower
temperature, but more heat because it has many more vibrating atoms. Which has greater total energy? The bathtub.
Temperature
Temperature is a measure of how fast the atoms in a material are vibrating. High temperature particles vibrate
faster than low temperature particles. Rapidly vibrating atoms smash together, which generates heat. As a material
cools down, the atoms vibrate more slowly and collide less frequently. As a result, they emit less heat. What is the
difference between heat and temperature?
• Temperature measures how fast a material’s atoms are vibrating.
• Heat measures the material’s total energy.
Thermal energy (heat) is the total amount of energy of motion of the particles in a substance.
MEDIA
Click image to the left for more content.
Bill Nye The Science Guy Video on Heat
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Heat
Heat energy is transferred between physical entities. Heat is taken in or released when an object changes state, or
changes from a gas to a liquid, or a liquid to a solid.
Summary and Vocabulary
• Temperature the speed of vibration of the molecules that make up a substance.
• Heat is the energy transferred between physical entities.
Practice
Use this resource to answer the questions that follow.
http://www.youtube.com/watch?v=v1zOnyC4RgQ
MEDIA
Click image to the left for more content.
1. What is temperature?
2. What determines heat?
3. How is temperature measured?
4. What is heat?
5. What is kinetic energy?
6. What does temperature measure?
Review
1. How does evaporative cooling work? Why do you think it is only effective in hot, dry areas?
2. What happens to the temperature of a substance as it changes state from liquid to solid? What happens to its latent
heat?
3. As a substance changes state from liquid to solid, what happens to the molecules that make it up?
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C HAPTER
Chapter 6. Heat Transfer in the Atmosphere
6
Heat Transfer in the
Atmosphere
• Explain how conduction and convection work in the atmosphere.
What could cause such a spectacular, swirling funnel of air?
For many people, this sight is unfamiliar. It is a tornado. Tornadoes happen when heat is rapidly transferred between
layers in the atmosphere.
Heat Transfer in the Atmosphere
Heat moves in the atmosphere the same way it moves through the solid Earth or another medium. What follows is a
review of the way heat flows, but applied to the atmosphere.
Radiation is the transfer of energy between two objects by electromagnetic waves. Heat radiates from the ground
into the lower atmosphere.
In conduction, heat moves from areas of more heat to areas of less heat by direct contact. Warmer molecules
vibrate rapidly and collide with other nearby molecules, transferring their energy. In the atmosphere, conduction is
more effective at lower altitudes, where air density is higher. This transfers heat upward to where the molecules are
spread further apart or transfers heat laterally from a warmer to a cooler spot, where the molecules are moving less
vigorously.
Heat transfer by movement of heated materials is called convection. Heat that radiates from the ground initiates
convection currents in the troposphere. As the particles of air are heated, they move more rapidly, bumping into each
other and moving further apart. As a result, the density of the warmed air becomes less dense and rises. Cooler,
more dense air then sinks to the surface of the Earth. (Figure 6.1).
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FIGURE 6.1
Thermal convection where the heat source is at the bottom and there is a ceiling at the top.
What Drives Atmospheric Circulation?
Different parts of the Earth receive different amounts of solar radiation. Which part of the planet receives the most
solar radiation? The Sun’s rays strike the surface most directly at the equator.
The difference in solar energy received at different latitudes drives atmospheric circulation.
Summary
• In conduction, substances must be in direct contact as heat moves from areas of more heat to areas of less
heat.
• In convection, materials move depending on their heat relative to nearby materials.
• The equator receives more solar energy than other latitudes.
Vocabulary
•
•
•
•
Radiation: transfer of energy by electromagnetic waves
Conduction: transfer of heat from one substance to another that are touching
Convection: transfer of heat by the movement of fluids
Convection currents: upward movement of warm air and downward movement of cold air in the troposphere
Practice
Use this resource to answer the questions that follow.
http://www.youtube.com/watch?v=ajQ3hm5JidU
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Chapter 6. Heat Transfer in the Atmosphere
MEDIA
Click image to the left for more content.
1. What powers our weather?
2. What does heat cause?
3. How does the tilt of the Earth affect heating?
4. What causes wind?
5. What occurs in the water?
Review
1. What is moving in conduction? What is moving in convection?
2. The poles experience 24 hours of daylight in their summer. Why do poles receive less solar radiation than the
equator?
3. What drives atmospheric circulation?
References
1. HSchmeling (Harroschmeling). . Public Domain
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C HAPTER
7 Heat Budget of Planet Earth
• Explain Earth’s heat budget and its relationship to solar radiation.
How does heat on Earth resemble a household budget?
The heat left on Earth is heat in minus heat out. If more energy comes into the system than goes out of the system,
the planet warms. If less energy goes into the system than goes out of the system, the planet cools. Replace the
word "money" for "heat" and "on Earth" to "in your bank account" and you describe a household budget. Of course,
Earth’s heat budget is a lot more complex than a simple household budget.
Heat at Earth’s Surface
About half of the solar radiation that strikes the top of the atmosphere is filtered out before it reaches the ground.
This energy can be absorbed by atmospheric gases, reflected by clouds, or scattered. Scattering occurs when a light
wave strikes a particle and bounces off in some other direction.
About 3% of the energy that strikes the ground is reflected back into the atmosphere. The rest is absorbed by rocks,
soil, and water and then radiated back into the air as heat. These infrared wavelengths can only be seen by infrared
sensors.
The basics of Earth’s annual heat budget are described in this video (4b): http://www.youtube.com/watch?v=mjj2i
3hNQF0&feature=related (5:40).
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Chapter 7. Heat Budget of Planet Earth
MEDIA
Click image to the left for more content.
The Heat Budget
Because solar energy continually enters Earth’s atmosphere and ground surface, is the planet getting hotter? The
answer is no (although the next section contains an exception), because energy from Earth escapes into space through
the top of the atmosphere. If the amount that exits is equal to the amount that comes in, then average global
temperature stays the same. This means that the planet’s heat budget is in balance. What happens if more energy
comes in than goes out? If more energy goes out than comes in?
To say that the Earth’s heat budget is balanced ignores an important point. The amount of incoming solar energy is
different at different latitudes. Where do you think the most solar energy ends up and why? Where does the least
solar energy end up and why? See Table 7.1
TABLE 7.1: The Amount of Incoming Solar Energy
Equatorial Region
Polar Regions
Day Length
Nearly the same all
year
Night 6 months
Sun Angle
High
Solar Radiation
High
Albedo
Low
Low
Low
High
Note: Colder temperatures mean more ice and snow cover the ground, making albedo relatively high.
This animation shows the average surface temperature across the planet as it changes through the year: Monthly
Mean Temperatures (http://upload.wikimedia.org/wikipedia/commons/b/b3/MonthlyMeanT.gif) .
The difference in solar energy received at different latitudes drives atmospheric circulation.
Summary
• Incoming solar radiation is absorbed by atmospheric gases, reflected by clouds, or scattered.
• Much of the radiation that strikes the ground is radiated back into the atmosphere as heat.
• More solar radiation strikes the equator than the poles.
Practice
Use this resource to answer the questions that follow.
http://www.youtube.com/watch?v=JFfD6jn_OvA
MEDIA
Click image to the left for more content.
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1. What does CERES measure?
2. What does the acronym CERES stand for?
3. What is the ideal radiation budget?
4. How much of the sun’s radiation is reflected?
5. How much energy does the ocean absorb?
6. What are scientists finding with CERES?
7. Why is the Earth warming?
8. What is a carbon footprint?
Review
1. If the Sun suddenly started to emit more energy, what would happen to Earth’s heat budget and the planet’s
temperature?
2. If more greenhouse gases were added to the atmosphere, what would happen to Earth’s heat budget and the
planet’s temperature?
3. What happens to sunlight that strikes the ground?
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C HAPTER
Chapter 8. Greenhouse Effect
8
Greenhouse Effect
• Describe the greenhouse effect.
• Explain how human actions contribute to the greenhouse effect.
How does the atmosphere resemble a greenhouse?
To extend the growing season, many farmers use greenhouses. A greenhouse traps heat so that days that might be too
cool for a growing plant can be made to be just right. Similar to a greenhouse, greenhouse gases in the atmosphere
keep Earth warm.
The Greenhouse Effect
The exception to Earth’s temperature being in balance is caused by greenhouse gases. But first the role of greenhouse
gases in the atmosphere must be explained.
Greenhouse gases warm the atmosphere by trapping heat. Some of the heat that radiates out from the ground is
trapped by greenhouse gases in the troposphere. Like a blanket on a sleeping person, greenhouse gases act as
insulation for the planet. The warming of the atmosphere because of insulation by greenhouse gases is called the
greenhouse effect (Figure 8.1). Greenhouse gases are the component of the atmosphere that moderate Earth’s
temperatures.
Greenhouse Gases
Greenhouse gases include CO2 , H2 O, methane, O3 , nitrous oxides (NO and NO2 ), and chlorofluorocarbons (CFCs).
All are a normal part of the atmosphere except CFCs. Table 8.1 shows how each greenhouse gas naturally enters the
atmosphere.
TABLE 8.1: Greenhouse Gas Entering the Atmosphere
Greenhouse Gas
Carbon dioxide
Methane
Nitrous oxide
Ozone
Chlorofluorocarbons
Where It Comes From
Respiration, volcanic eruptions, decomposition of plant
material; burning of fossil fuels
Decomposition of plant material under some conditions, biochemical reactions in stomachs
Produced by bacteria
Atmospheric processes
Not naturally occurring; made by humans
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FIGURE 8.1
The Earth’s heat budget shows the
amount of energy coming into and going
out of the Earth’s system and the importance of the greenhouse effect. The
numbers are the amount of energy that
is found in one square meter of that location.
Different greenhouse gases have different abilities to trap heat. For example, one methane molecule traps 23 times
as much heat as one CO2 molecule. One CFC-12 molecule (a type of CFC) traps 10,600 times as much heat as one
CO2 . Still, CO2 is a very important greenhouse gas because it is much more abundant in the atmosphere.
Human Activity and Greenhouse Gas Levels
Human activity has significantly raised the levels of many of greenhouse gases in the atmosphere. Methane levels
are about 2 1/2 times higher as a result of human activity. Carbon dioxide has increased more than 35%. CFCs have
only recently existed.
What do you think happens as atmospheric greenhouse gas levels increase? More greenhouse gases trap more
heat and warm the atmosphere. The increase or decrease of greenhouse gases in the atmosphere affect climate and
weather the world over.
This PowerPoint review, Atmospheric Energy and Global Temperatures, looks at the movement of energy through
the atmosphere (6a): http://www.youtube.com/watch?v=p6xMF_FFUU0 (8:17).
MEDIA
Click image to the left for more content.
Summary
• Greenhouse gases include CO2 , H2 O, methane, O3 , nitrous oxides (NO and NO2 ), and chlorofluorocarbons
(CFCs).
• Tropospheric greenhouse gases trap heat in the atmosphere; greenhouse gases vary in their heat-trapping
abilities.
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Chapter 8. Greenhouse Effect
• Levels of greenhouse gases in the atmosphere are increasing due to human activities.
Vocabulary
• Greenhouse effect: the warming of the atmosphere because of insulation from greenhouse gases
Practice
Use this resource to answer the questions that follow.
http://www.hippocampus.org/Earth Science → Environmental Science → Search: Greenhouse Effects (first resource, starts with "About 50% of solar radiation...")
1. How much solar radiation is absorbed by the surface of the Earth?
2. What reflects the radiation?
3. How is most radiation re-emitted?
4. What is the net effect of this heating?
5. What are the primary greenhouse gases?
Review
1. If you were trying to keep down global temperature and you had a choice between adding 100 methane molecules
or 1 CFC-12 molecule to the atmosphere, which would you choose?
2. What is the greenhouse effect?
3. How does Earth’s atmosphere resemble a greenhouse?
References
1. Robert A. Rohde/Global Warming Art. . GNU-FDL 1.2
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C HAPTER
9
Circulation in the
Atmosphere
• Explain why atmospheric circulation occurs.
Why do we say Earth’s temperature is moderate?
It may not look like it, but various processes work to moderate Earth’s temperature across the latitudes. Atmospheric
circulation brings warm equatorial air poleward and frigid polar air toward the equator. If the planet had an
atmosphere that was stagnant, the difference in temperature between the two regions would be much greater.
Air Pressure Zones
Within the troposphere are convection currents (cells). (Figure 9.1). Air heated at the ground rises, creating a low
pressure zone. Air from the surrounding area is sucked into the space left by the rising air. Air flows horizontally
at top of the troposphere; horizontal flow is called advection. The air cools until it descends. When the air reaches
the ground, it creates a high pressure zone. Air flowing from areas of high pressure to low pressure creates winds.
The greater the pressure difference between the pressure zones, the faster the wind blows.
Warm air can hold more moisture than cool air. When warm air rises and cools in a low pressure zone, it may not
be able to hold all the water it contains as vapor. Some water vapor may condense to form clouds or precipitation.
When cool air descends, it warms. Since it can then hold more moisture, the descending air will evaporate water on
the ground.
Wind
Air moving between large high and low pressure systems at the bases of the three major convection currents creates
the global wind belts. These planet-wide air circulation systems profoundly affect regional climate. Smaller pressure
systems create localized winds that affect the weather and climate of a local area.
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Chapter 9. Circulation in the Atmosphere
FIGURE 9.1
Warm air rises, creating a low pressure zone; cool air sinks, creating a
high pressure zone.
An online guide to air pressure and winds from the University of Illinois is found here: http://ww2010.atmos.uiuc
.edu/%28Gh%29/guides/mtr/fw/home.rxml.
Atmospheric Circulation
Two Convection Currents
Because more solar energy hits the equator, the air warms and forms a low pressure zone. At the top of the
troposphere, half moves toward the North Pole and half toward the South Pole. As it moves along the top of
the troposphere it cools. The cool air is dense, and when it reaches a high pressure zone it sinks to the ground. The
air is sucked back toward the low pressure at the equator. This describes the convection cells north and south of the
equator.
Plus Coriolis Effect
If the Earth did not rotate, there would be one convection current (cell) in the northern hemisphere and one in the
southern with the rising air at the equator and the sinking air at each pole. But because the planet does rotate, the
situation is more complicated. The planet’s rotation means that the Coriolis effect must be taken into account. The
winds curve.
Let’s look at atmospheric circulation in the Northern Hemisphere as a result of the Coriolis effect (Figure 9.2). Air
rises at the equator, but as it moves toward the pole at the top of the troposphere, it deflects to the right. (Remember
that it just appears to deflect to the right because the ground beneath it moves.) At about 30o N latitude, the air from
the equator meets air flowing toward the equator from the higher latitudes. This air is cool because it has come from
higher latitudes. Both batches of air descend, creating a high pressure zone. Once on the ground, the air returns to
the equator. This convection cell is called the Hadley Cell and is found between 0o and 30o N.
Equals Three Convection Cells
There are two more convection currents (cells) in the Northern Hemisphere. The Ferrell cell is between 30o N and
50o to 60o N. This cell shares its southern, descending side with the Hadley cell to its south. Its northern rising limb
is shared with the Polar cell located between 50o N to 60o N and the North Pole, where cold air descends.
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FIGURE 9.2
The atmospheric circulation cells, showing direction of winds at Earth’s surface.
Plus Three in the Southern Hemisphere
There are three mirror image circulation cells in the Southern Hemisphere. In that hemisphere, the Coriolis effect
makes objects appear to deflect to the left. The total number of atmospheric circulation cells around the globe is six.
Summary
• The atmosphere has six major convection currents, three in the northern hemisphere and three in the southern.
• Coriolis effect results in there being three convection currents per hemisphere rather than one.
• Winds blow at the base of the atmospheric convection cells.
Vocabulary
• Convection currents: the circulation of a fluid as it heats up and cools down
Practice
Use this resource to answer the questions that follow.
http://www.youtube.com/watch?v=DHrapzHPCSA
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Chapter 9. Circulation in the Atmosphere
MEDIA
Click image to the left for more content.
1. Where is insolation strongest?
2. What type of pressure occurs at the equator?
3. What type of pressure occurs at the poles?
4. What are Hadley cells?
5. Where does convection occur?
6. How do surface winds move?
7. What is the polar front?
8. How does air move at high altitudes?
Review
1. Diagram and label the parts of a convection cell in the troposphere.
2. How many major atmospheric convection cells would there be without Coriolis effect? Where would they be?
3. How does Coriolis effect change atmospheric convection?
References
1. CK-12 Foundation. . CC-BY-NC-SA 3.0
2. Hastings. . CC-BY-SA 1.0
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C HAPTER
10
Local Winds
• Describe the types of local winds and how they are created.
• Explain how local winds influence a region’s environment.
Which large rainstorms are crucial for people in some parts of the world?
India, Pakistan, and other nations in southern Asia are great places to go to see monsoon rains. The region depends
on the water they bring. Parts of the Southwestern United States also receive monsoon rains. These rains break the
summer heat. They also provide water to desert plants. With winter rains and summer rains, these deserts are more
lush than many.
Local Winds
Local winds are winds that blow over a limited area. Local winds blow between small low and high pressure systems.
They are influenced by local geography. Nearness to an ocean, lake, or mountain range can affect local winds. Some
examples are found below. Local winds can affect the weather and climate of a region.
Land and Sea Breezes
Ocean water is slower to warm up and cool down than land. So the sea surface is cooler than the land in the daytime.
It is also cooler than the land in the summer. The opposite is also true. The water stays warmer than the land during
the night and the winter. These differences in heating cause local winds known as land and sea breezes (Figure
10.1).
• A sea breeze blows from sea to land during the day or in summer. That’s when air over the land is warmer
than air over the water. The warm air rises. Cool air from over the water flows in to take its place.
• A land breeze blows from land to sea during the night or in winter. That’s when air over the water is warmer
than air over the land. The warm air rises. Cool air from the land flows out to take its place.
Monsoons
Monsoons are like land and sea breezes, but on a larger scale. They occur because of seasonal changes in the
temperature of land and water. In the winter, they blow from land to water. In the summer, they blow from water
to land. In regions that experience monsoons, the seawater offshore is extremely warm. The hot air absorbs a lot
of the moisture and carries it over the land. Summer monsoons bring heavy rains on land. Monsoons occur in
several places around the globe. The most important monsoon in the world is in southern Asia (Figure 10.2). These
monsoons are important because they carry water to the many people who live there.
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Chapter 10. Local Winds
FIGURE 10.1
Land and sea breezes blow because of daily differences in heating.
Mountain and Valley Breezes
The air on a mountain slope warms more than the air over the nearby valley. The warm air rises and brings cool air
up from below. This is a valley breeze. At night the mountain slope cools more than the air over the valley. The air
flows downhill creating a mountain breeze.
Katabatic Winds
Katabatic winds move the same way as mountain and valley breezes. However, they are much stronger. Katabatic
winds form over a high plateau that is surrounded by mountains. In winter, the plateau grows cold. Air sinks through
the gaps in the mountains. Over Antarctica and Greenland, these winds are frigid.
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FIGURE 10.2
Monsoons blow over southern Asia.
Chinook Winds
Chinook winds (Figure 10.3) occur when air is forced over a mountain range. Warm air rises over the Sierra
Nevada in California, for example, because it is pushed eastward by the westerly winds. The air cools as it rises and
precipitates. The air is now dry. It sinks down the far side of the mountains and may create strong winds. These
Chinook winds are relatively warm. If there is snow, the winds may melt it quickly. The dry sinking air creates a
rainshadow effect. Rainshadow effect is responsible for many of the world’s deserts.
FIGURE 10.3
As air rises over a mountain it cools
and loses moisture. The air warms by
compression on the leeward side. The
resulting warm and dry winds are Chinook
winds. The leeward side of the mountain
experiences rainshadow effect.
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Chapter 10. Local Winds
Santa Ana Winds
Santa Ana winds (Figure 10.4) are responsible for many large fires in Southern California (Figure 10.5). The
Santa Ana winds arrive at the end of California’s long summer drought season. Air east of the Sierra Nevada
Mountains cools in late fall. This creates a high pressure zone. The air is then forced downhill through the deserts
of the Southwest. It blows westward toward the ocean. The air is blocked by the San Gabriel and San Bernardino
Mountains. So it is funneled rapidly through the mountain passes. If a fire starts, it spreads quickly. The result is
large-scale devastation.
FIGURE 10.4
The winds are especially fast through
Santa Ana Canyon, for which they are
named. Santa Ana winds blow dust and
smoke westward over the Pacific from
Southern California.
FIGURE 10.5
In October 2007, Santa Ana winds fueled
many fires that together burned 426,000
acres of wild land and more than 1,500
homes in Southern California.
Desert Winds
High summer temperatures on the desert create high winds and monsoon storms. Strong winds in the desert can pick
up dust and blow it around. A dust storm known as a haboob (Figure 10.6) forms in the downdrafts on the front of
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a thunderstorm.
FIGURE 10.6
A haboob in the Phoenix metropolitan
area, Arizona.
Vocabulary
• land breeze: Wind that blows from land to sea in winter when the ocean is warmer than the land.
• sea breeze: Wind that blows from sea to land in summer when the land is warmer than the ocean.
Summary
• Local winds blow between high pressure and low pressure areas.
• Winds blow up and down slope, on and off land and sea, through deserts or over mountain passes.
• Some local winds are well known in an area: haboobs in the desert, Santa Ana winds in Southern California,
Chinook winds in Colorado.
Practice
Use the resources below to answer the questions that follow.
• Chinook Winds: The Snow Eaters at http://www.youtube.com/watch?v=VEJmQglWnQY (1:16)
MEDIA
Click image to the left for more content.
1. What are Chinook winds?
2. Where do Chinook winds occur?
3. Explain how Chinook winds work.
• Santa Ana Winds at http://www.youtube.com/watch?v=Dq1f1VAKXSw (1:15)
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Chapter 10. Local Winds
MEDIA
Click image to the left for more content.
4.
5.
6.
7.
8.
What are the Santa Ana winds?
Where do the Santa Ana winds occur?
What causes the Santa Ana winds?
Explain how the Santa Ana winds affect the weather.
What can be caused by the Santa Ana winds?
Review
1. What causes local winds to blow?
2. Describe valley breezes and mountain breezes. How are they an example of how local winds form?
3. How do Chinook winds lead to rainshadow effect?
References
1. CK-12 Foundation - Christopher Auyueng. . CC-BY-NC-SA 3.0
2. Map courtesy of the Central Intelligence Agency’s World Factbook; modified by CK-12 Foundation - Hana
Zavadska. . Public Domain
3. Courtesy of US Federal Aviation Administration. . Public Domain
4. Courtesy of NASA. . Public Domain
5. Image copyright Peter Weber, 2012. . Used under license from Shutterstock.com
6. Image copyright Chris Curtis, 2012. . Used under license from Shutterstock.com
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C HAPTER
11
• Explain how global winds form.
• Explain how global winds influence climate.
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Global Wind Belts
www.ck12.org
Chapter 11. Global Wind Belts
How did the "trade winds" get their name?
Not so long ago ships could only sail in the direction the wind was blowing, more-or-less. For centuries, a trip could
be made or broken by how hard the wind blew. The trade winds were named because they were a reliable way to get
across the ocean. Ships engaged in trade needed these winds to take or leave goods. The trade winds are one of the
global wind belts.
Global Winds
Global winds are winds that occur in belts that go all around the planet (Figure 11.1). Like local winds, global
winds are caused by unequal heating of the atmosphere. At the equator, there is little to know wind. This is referred
to as the doldrums.
FIGURE 11.1
Global winds occur in belts around the
globe.
Heating and Global Winds
Earth is hottest at the equator and gets cooler toward the poles. The differences in heating create huge convection
currents in the troposphere. At the equator, for example, warm air rises up to the tropopause. When it can’t rise any
higher, it flows north or south.
By the time the moving air reaches 30° N or °S latitude, it has cooled somewhat. The cool air sinks to the surface.
Then it flows over the surface back to the equator. Other global winds occur in much the same way. There are three
enormous convection cells north of the equator and three south of the equator.
Global Winds and the Coriolis Effect
Earth is spinning as air moves over its surface. This causes the Coriolis effect. Winds blow on a diagonal over the
surface due to Coriolis effect. From which direction do the northern trade winds blow?
Without the Coriolis effect the global winds would blow north to south or south to north. But the Coriolis effect
makes them blow northeast to southwest or the reverse in the northern hemisphere. The winds blow northwest to
southeast or the reverse in the southern hemisphere.
The wind belts have names. The Trade Winds are nearest the equator. The next belt is the prevailing westerlies.
After the prevailing westerlies, are the horse latitudes, which is another area of calm before the polar easterlies.
Finally are the polar easterlies. The names are the same in both hemispheres.
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Jet Streams
Jet streams are fast-moving air currents high in the troposphere. They are also the result of unequal heating of the
atmosphere. Jet streams circle the planet, mainly from west to east. The strongest jet streams are the polar jets.
PIctured below is the northern polar jet (Figure 11.2).
FIGURE 11.2
This jet stream helps planes fly quickly
from west to east over North America.
How do you think it affects planes that fly
from east to west?
Vocabulary
• Global winds: Winds that occur in belts that go all around the planet.
• jet stream: Fast-flowing river of air high in the atmosphere; jet streams are found where two very different air
masses move past each other.
• trade winds: main global winds around the equator
• polar easterlies: winds nearest to North and South Poles
• prevailing westerlies: winds between trade winds and polar easterlies
• Doldrums: calm area where there are no winds (equator)
• Horse latitutdes: 30 degrees North and South; an area of little to no wind
Summary
• Global winds blow from high to low pressure at the base of the atmospheric circulation cells.
• The globe has six atmospheric circulation cells. Three are north of the equator and three are south. These cells
have names.
• Jet streams are fast moving rivers of air going in opposite directions.
Practice
Use the resource below to answer the questions that follow.
• Wind Patterns at http://www.youtube.com/watch?v=IWjeHtdpFjE (2:43)
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Chapter 11. Global Wind Belts
MEDIA
Click image to the left for more content.
1.
2.
3.
4.
5.
6.
7.
What creates wind?
What are monsoons? How are they created?
What are local and regional winds?
What are the global wind patterns?
In what direction does the Earth rotate?
What is the Coriolis effect?
What are the Westerlies?
Review
1. What is a jet stream? What is "the" jet stream?
2. Which takes longer: a flight from San Francisco to Philadelphia or a flight from Philadelphia to San Francisco?
Why did you make that choice?
3. Describe the locations of the major atmospheric convection cells. What creates them?
References
1. CK-12 Foundation - Christopher Auyeung. . CC-BY-NC-SA 3.0
2. Courtesy of US Centennial of Flight Commission/NASA. . Public Domain
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