Earth’s Weather and Climate -Heat Transfer (Comp Sci I)

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www.ck12.org Chapter 1. Earth’s Weather and Climate - Heat Transfer (Comp Sci I)

CHAPTER 1 Earth’s Weather andClimate - Heat Transfer (Comp Sci I)

CHAPTER OUTLINE

1.1 Energy in the Atmosphere

1.2 Air Movement

1.3 References

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1.1. Energy in the Atmosphere www.ck12.org

1.1 Energy in the Atmosphere

Lesson Objectives

• Define energy.• Describe solar energy.• State how heat moves through the atmosphere.• Describe how solar energy varies across Earth’s surface.• Explain the greenhouse effect.

Vocabulary

• electromagnetic spectrum• energy• greenhouse effect• greenhouse gas• infrared light• photon• ultraviolet (UV) light• visible light

Introduction

Picture yourself sitting by the campfire in Figure 1.1. You and your friends are using the fire to heat soup in a pot.As the Sun goes down, the air gets chilly. You move closer to the fire. Heat from the fire warms you. Light from thefire allows you to see your friends.

FIGURE 1.1These campers can feel and see the en-ergy of their campfire.

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What Is Energy?

What explains all of these events? The answer can be summed up in one word: energy. Energy is defined as theability to do work. Doing anything takes energy. A campfire obviously has energy. You can feel its heat and see itslight.

Forms of Energy

Heat and light are forms of energy. Other forms are chemical and electrical energy. Energy can’t be created ordestroyed. It can change form. For example, a piece of wood has chemical energy stored in its molecules. When thewood burns, the chemical energy changes to heat and light energy.

Movement of Energy

Energy can move from one place to another. It can travel through space or matter. That’s why you can feel the heatof a campfire and see its light. These forms of energy travel from the campfire to you.

Energy from the Sun

Almost all energy on Earth comes from the Sun. The Sun’s energy heats the planet and the air around it. Sunlightalso powers photosynthesis and life on Earth.

Photons of Energy

The Sun gives off energy in tiny packets called photons. Photons travel in waves. Figure 1.2 models a wave oflight. Notice the wavelength in the figure. Waves with shorter wavelengths have more energy.

FIGURE 1.2This curve models a wave. Based on thisfigure, how would you define wavelength?

Electromagnetic Spectrum

Energy from the Sun has a wide range of wavelengths. The total range of energy is called the electromagneticspectrum. You can see it in Figure 1.3.

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FIGURE 1.3Compare the wavelengths of radio wavesand gamma rays. Which type of wave hasmore energy?

Visible light is the only light that humans can see. Different wavelengths of visible light appear as differentcolors. Radio waves have the longest wavelengths. They also have the least amount of energy. Infrared lighthas wavelengths too long for humans to see, but we can feel them as heat. The atmosphere absorbs the infrared light.Ultraviolet (UV) light is in wavelengths too short for humans to see. The most energetic UV light is harmful to life.The atmosphere absorbs most of this UV light from the Sun. Gamma rays have the highest energy and they are themost damaging rays. Fortunately, gamma rays don’t penetrate Earth’s atmosphere.

How Energy Moves Through the Atmosphere

Energy travels through space or material. Heat energy is transferred in three ways: radiation, conduction, andconvection.

Radiation

Radiation is the transfer of energy by waves. Energy can travel as waves through air or empty space. The Sun’senergy travels through space by radiation. After sunlight heats the planet’s surface, some heat radiates back into theatmosphere.

Conduction

In conduction, heat is transferred from molecule to molecule by contact. Warmer molecules vibrate faster than coolerones. They bump into the cooler molecules. When they do they transfer some of their energy. Conduction happensmainly in the lower atmosphere. Can you explain why?

Convection

Convection is the transfer of heat by a current. Convection happens in a liquid or a gas. Air near the ground iswarmed by heat radiating from Earth’s surface. The warm air is less dense, so it rises. As it rises, it cools. The cool

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air is dense, so it sinks to the surface. This creates a convection current, like the one in Figure 1.4. Convection isthe most important way that heat travels in the atmosphere.

FIGURE 1.4Convection currents are the main way that heat moves through theatmosphere. Why does warm air rise?

Energy and Latitude

Different parts of Earth’s surface receive different amounts of sunlight. You can see this in Figure 1.5. The Sun’srays strike Earth’s surface most directly at the equator. This focuses the rays on a small area. Near the poles, theSun’s rays strike the surface at a slant. This spreads the rays over a wide area. The more focused the rays are, themore energy an area receives and the warmer it is.

FIGURE 1.5The lowest latitudes get the most energyfrom the Sun. The highest latitudes getthe least.

How do the differences in energy striking different latitudes affect Earth? The planet is much warmer at the equatorthan at the poles. In the atmosphere, the differences in heat energy cause winds and weather. On the surface, thedifferences cause ocean currents. Can you explain how?

The Greenhouse Effect

When sunlight heats Earth’s surface, some of the heat radiates back into the atmosphere. Some of this heat isabsorbed by gases in the atmosphere. This is the greenhouse effect, and it helps to keep Earth warm. The greenhouseeffect allows Earth to have temperatures that can support life.

Gases that absorb heat in the atmosphere are called greenhouse gases. They include carbon dioxide and water vapor.Human actions have increased the levels of greenhouse gases in the atmosphere. This is shown in Figure 1.6. Theadded gases have caused a greater greenhouse effect. How do you think this affects Earth’s temperature?

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FIGURE 1.6Human actions have increased the natu-ral greenhouse effect.

Lesson Summary

• Energy is the ability to do work. Heat and light are forms of energy. Energy can change form. It can alsomove from place to place.

• Earth gets its energy from the Sun. The Sun gives off photons of energy that travel in waves. All thewavelengths of the Sun’s energy make up the electromagnetic (EM) spectrum.

• Energy moves in three ways. By radiation, it travels in waves across space. By conduction, it moves betweenmolecules that are in contact. By convection, it moves in a current through a liquid or gas.

• Energy from the Sun is more focused at the equator than the poles. Differences in energy by latitude causewinds and weather.

• Greenhouse gases in the atmosphere absorb heat. This is called the greenhouse effect and it makes the planetwarmer. Human actions have increased the greenhouse effect.

Lesson Review Questions

Recall

1. Define energy. List three forms of energy.

2. Describe the electromagnetic spectrum.

3. How is wavelength related to the energy of light?

4. What is the greenhouse effect?

5. List two greenhouse gases.

Apply Concepts

6. Look at Figure 1.1. Apply lesson concepts to explain three ways that heat from the campfire can travel.

Think Critically

7. Why is Earth colder at the poles than the equator?

8. Explain how human actions have increased the greenhouse effect.

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Points to Consider

Energy from the Sun heats the air in Earth’s atmosphere. You might predict that air temperature would increasesteadily with altitude. After all, the higher you go, the closer you are to the Sun. But it’s not that simple.

• Besides the Sun, what might heat up the atmosphere?• How do you think air temperature might change with altitude?

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1.2 Air Movement

Lesson Objectives

• Explain why air moves.• Identify causes of local winds.• Describe global winds and jet streams.

Vocabulary

• global wind• jet stream• land breeze• local wind• monsoon• sea breeze• wind

Introduction

Whether it’s a gentle breeze or strong wind, you are most aware of air when it moves. You can feel its moleculespress against you. You can also see the effects of air movement. Figure 1.7 shows some examples.

FIGURE 1.7How can you tell the wind is blowing in these photos?

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Why Air Moves

Air movement takes place in the troposphere. This is the lowest layer of the atmosphere. Air moves because ofdifferences in heating. These differences create convection currents and winds. Figure 1.8 shows how this happens.

• Air in the troposphere is warmer near the ground. The warm air rises because it is light. The light, rising aircreates an area of low air pressure at the surface.

• The rising air cools as it reaches the top of the troposphere. The air gets denser, so it sinks to the surface. Thesinking, heavy air creates an area of high air pressure near the ground.

• Air always flows from an area of higher pressure to an area of lower pressure. Air flowing over Earth’s surfaceis called wind. The greater the difference in pressure, the stronger the wind blows.

FIGURE 1.8Differences in air temperature cause con-vection currents and wind.

Local Winds

Local winds are winds that blow over a limited area. They are influenced by local geography. Nearness to an ocean,lake or mountain range can affect local winds. Some examples are found below.

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 duringthe night and the winter. These differences in heating cause local winds known as land and sea breezes. Land andsea breezes are illustrated in Figure 1.9.

• A sea breeze blows from sea to land during the day or in summer. That’s when air over the land is warmerthan 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 warmerthan air over the land. The warm air rises. Cool air from the land flows out to take its place.

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FIGURE 1.9Land and sea breezes blow because of daily differences in heating.

Monsoons

Monsoons are like land and sea breezes, but on a larger scale. They occur because of seasonal changes in thetemperature of land and water. In the winter, they blow from land to water. In the summer, they blow from waterto land. In regions that experience monsoons, the seawater offshore is extremely warm. The hot air absorbs a lot ofthe moisture and carries it over the land. Summer monsoons bring heavy rains on land. Monsoons occur in severalplaces around the globe. The most important monsoon in the world is in southern Asia, as shown in Figure 1.10.These monsoons are important because they carry water to the many people who live there.

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FIGURE 1.10Monsoons blow over southern Asia.

Global Winds

Global winds are winds that occur in belts that go all around the planet. You can see them in Figure 1.11. Likelocal winds, global winds are caused by unequal heating of the atmosphere.

FIGURE 1.11Global winds occur in belts around theglobe.

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Heating and Global Winds

Earth is hottest at the equator and gets cooler toward the poles. The differences in heating create huge convectioncurrents in the troposphere. At the equator, for example, warm air rises up to the tropopause. It can’t rise any higher,so it flows north or south.

By the time the moving air reaches 30° N or S latitude, it has cooled. The cool air sinks to the surface. Then it flowsover the surface back to the equator. Other global winds occur in much the same way. There are three enormousconvection 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 thesurface, instead of due north or south. From which direction do the northern trade winds blow?

Without Coriolis Effect the global winds would blow north to south or south to north. But Coriolis makes them blownortheast to southwest or the reverse in the Northern Hemisphere. The winds blow northwest to southeast or thereverse in the southern hemisphere.

The wind belts have names. The Trade Winds are nearest the equator. The next belt is the westerlies. Finally are thepolar easterlies. The names are the same in both hemispheres.

Jet Streams

Jet streams are fast-moving air currents high in the troposphere. They are also the result of unequal heating of theatmosphere. Jet streams circle the planet, mainly from west to east. The strongest jet streams are the polar jets. Thenorthern polar jet is shown in Figure 1.12.

FIGURE 1.12This jet stream helps planes fly quicklyfrom west to east over North America.How do you think it affects planes that flyfrom east to west?

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Lesson Summary

• Air movement takes place in the troposphere. Air moves because of differences in heating. The differencescreate convection currents and winds.

• Local winds are winds that blow over a limited area. They are influenced by local geography, such as nearnessto an ocean. They include land and sea breezes as well as monsoons.

• Global winds occur in belts around the globe. They are caused by unequal heating of Earth’s surface. TheCoriolis effect causes global winds to blow on a diagonal over the surface. Unequal heating also causes jetstreams high in the troposphere.

Lesson Review Questions

Recall

1. Define wind.

2. What are local winds?

3. Describe monsoons.

4. Why are summer monsoons likely to bring heavy rains?

5. How does the Coriolis effect influence global winds?

Apply Concepts

6. In Figure 1.11, find the global winds called prevailing westerlies. They blow over most the U.S. Apply lessonconcepts to explain the direction these winds blow.

Think Critically

7. Explain how differences in heating cause wind.

8. Compare and contrast land and sea breezes with monsoons.

9. If changes in the atmosphere caused the Indian Ocean to cool down, how would the people of southern Asia beaffected? What might be the result?

Points to Consider

Temperature differences in the atmosphere cause winds. They also cause other weather conditions, such as cloudsand rain.

• How do temperature differences cause clouds to form?• How do they affect precipitation?

Earth’s WEather and Climate - Heat Transfer

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1.3. References www.ck12.org

1.3 References

1. Image copyright Anton Gvozdikov, 2013. http://www.shutterstock.com . Used under license from Shutter-stock.com

2. Courtesy of NASA. http://science.hq.nasa.gov/kids/imagers/ems/waves3.html . Public Domain3. Courtesy of NASA; modified by CK-12 Foundation. http://www.centennialofflight.gov/essay/Dictionary/E

LECTROSPECTRUM/DI159G1.jpg . Public Domain4. Hana Zavadska. CK-12 Foundation . CC BY-NC 3.05. Laura Guerin. CK-12 Foundation . CC BY-NC 3.06. Courtesy of Will Elder/National Park Service. http://www.nps.gov/goga/naturescience/climate-change-cau

ses.htm . Public Domain7. From left to right: Julian Lim (Flickr:julianlimjl); Nico Nelson; Euan Morrison (Flickr:euan1234). From

left to right: http://www.flickr.com/photos/julianlim/4838480578/; http://www.flickr.com/photos/niconelson/4289796215/; http://www.flickr.com/photos/euanzkamera/7909241274/ . CC BY 2.0

8. Christopher Auyeung. CK-12 Foundation . CC BY-NC 3.09. Christopher Auyeung. CK-12 Foundation . CC BY-NC 3.0

10. Map courtesy of the Central Intelligence Agency’s World Factbook; modified by CK-12 Foundation. http://commons.wikimedia.org/wiki/File:Asia-map.png . Public Domain

11. Christopher Auyeung. CK-12 Foundation . CC BY-NC 3.012. Laura Guerin, based on image by US Centennial of Flight Commission/NASA. CK-12 Foundation (based on

image at http://commons.wikimedia.org/wiki/File:Jet_Stream.jpg) . CC BY-NC 3.0

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