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Solar Energy, Seasons, & the Atmosphere1 Energy & Earth Systems

We follow incoming solar energy from the Sun to the top of Earth’s atmosphere, and then follow that energy as it drives Earth’s physical systems and influences our daily lives. This solar energy, along with Earth’s tilt and rotation, produce the seasonal patterns of changing day length and Sun angle. The Sun is the ultimate energy source for most life processes in our biosphere.

We examine the atmosphere’s composition, temperature, and function. Our look at the atmosphere also includes the spatial aspects of both natural and human-produced air pollution. We all interact with the atmosphere with each breath we take and in many other ways. For example, burning fossil fuels to generate electricity and power our cars and planes releases vast quantities of carbon dioxide gas into the atmosphere. These topics are essential to physical geography, for we are influencing the atmospheric composition for the future.

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Key Concepts & Topics

Sunrise over the Pacific Ocean, as photographed from an altitude of 419 km (260 mi.) by Astro- naut Reid Wiseman aboard the International Space Station on September 1, 2014 . We are see- ing Earth’s atmosphere from the side, as well as Earth’s curvature. The different colors correspond to different layers in the atmo- sphere. This image highlights how thin our atmosphere is.

1 What is the origin & structure of our solar system?

1.1 Our Galaxy and Solar System 1.2 Energy from the Sun 1.3 Electromagnetic Spectrum 1.4 Incoming Energy and Net Radiation

2 Why do we have seasons?

1.5 The Seasons

3 What are the properties of our atmosphere?

1.6 Atmospheric Composition 1.7 Atmospheric Temperature 1.8 The Atmosphere’s Functional Layers 1.9 Variable Atmospheric Components 1.10 Anthropogenic Pollution

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Key Learning Concepts ▶ Distinguish among galaxies, stars, and planets. ▶ Differentiate between the key distances of our solar system,

and locate Earth.

What is the origin & structure of our solar system?

1.1 Our Galaxy & Solar System

Earth’s Place in Space Our solar system is located on one of the outer “arms” of the Milky Way Galaxy, a disk-shaped spiral of stars (▶ Fig. 1.1). From our Earth-bound perspective in the Milky Way, the galaxy appears to stretch across the night sky like a narrow band of hazy light, although our eyes can see only a few thousand of these billions of stars. Our Sun is just one of 300 billion stars in the Milky Way Galaxy. The universe has at least 125 billion galaxies, each of which contains hundreds of billions of stars.

Our solar system condensed from a huge, slowly rotat- ing and collapsing cloud of dust and gas, a nebula. Gravity, the mutual attraction exerted by every object upon all other objects in proportion to their mass, was the key force in this condensing solar nebula. The beginnings of the forma- tion of the Sun and its solar system are estimated to have occurred more than 4.6 billion years ago. Within a nebula, stars condense from clouds of gas and dust, with planets gradually forming in orbits about the central mass. Astrono- mers study this process in other parts of the galaxy, where more than 1800 planets have been observed orbiting distant stars. An initial estimate of the number of planets in the Milky Way is 100 billion. Astronomers think there could be 500 million of these planets in the habitable zones with moderate temperatures where water can exist as a liquid.

Physical geography focuses on planet Earth. But Earth is not alone in space, and its set-

ting within the vastness of the universe affects conditions and processes in Earth systems.

What is the key difference between a galaxy and a solar system?

geoCheCK✔

Animation Earth Sun Relations

http://goo.gl/XVJd3y

Our Solar Systems is in the Orion Spur of the Sagittarius Arm.

100,000 light-years

▲ 1.1 The Milky Way Galaxy (a) The overal structure of our galaxy. (b) The Milky Way as seen from Earth.

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1 Solar Energy, Seasons, & the Atmosphere 5

Dimensions, Distances, & Earth’s Orbit One way to think about Earth’s place in relation to the solar sys- tem and galaxy is to use the speed of light as a yardstick to meas- ure the distances involved. The speed of light is 300,000 kmps (kilometers per second), or 186,000 mps (miles per second). The tremendous distance that light travels in a year, 9.5 trillion

Earth is farthest from the Sun, during the Northern Hemisphere summer on July 4 at 152,100,000 km (94,500,000 mi).

Earth is closest to the Sun during the Northern Hemisphere winter on January 3 at 147,100,000 km (91,400,000 mi).

MercuryMercury Venus

Jupiter

Sun Asteroid belt

Neptune

Solar System is 11 light-hours wide

Uranus

Saturn

Sun MercuryMercuryVenus

Earth

Mars

Earth’s elliptical orbit around the Sun

(a)

(b)

Earth

Mars

▲ 1.2 Our solar system and Earth’s orbit

What is the speed of light?geoCHECK✔

1. How did the solar system form from a nebula? 2. What is the diameter of our solar system? The distance across the

known universe? 3. How much does the distance from Earth to the Sun vary over a year?

How does this distance compare to the average distance from Earth to the Sun?

geoQUIZ

kilometers (6 trillion miles), is known as a light-year, and it is used as a unit of measurement for the vast universe.

The Milky Way is about 100,000 light-years from side to side, and the known universe stretches approximately 12 billion light- years in all directions. In contrast, our entire solar system is ap- proximately 11 hours in diameter, if measured by the speed of light

(◀ Fig. 1.2a). The Moon is an average of 384,400 km (238,866 mi) from Earth, or about 1.28 seconds away at the speed of light.

Earth’s orbit around the Sun is an oval or elliptical path. The average distance from Earth to the Sun is ap- proximately 150 million kilometers (93 million miles), so light from the Sun reaches Earth in about 8 minutes and 20 seconds. While Earth is closer to the Sun in January (147,100,000 km, 91,400,000 mi) than in July (152,100,000 km, 94,500,000 mi), causing a slight variation in the amount of solar energy received, it is not enough to cause seasonal changes (◀ Fig. 1.2b).

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6 What is the origin & structure of our solar system?

1.2 Energy from the Sun

Relative size of Earth

(a) Solar eruption, December 31, 2012

(b) Sunspot maximum in 2000 and minimum in 2009 ▲ 1.3 Solar coronal mass eruption and sunspots

Why is the Sun hot?geoCHECK✔

Solar Activity & Solar Wind How does the Sun generate all of this energy? To gen- erate enormous energy, you need matter—lots of it. The Sun captured about 99.9% of the matter from the original solar nebula. All the planets, their satellites, as- teroids, comets, and debris are made up of the remain- ing 0.1%. In our entire solar system, the Sun is the only object having the enormous mass needed to sustain a nuclear reaction in its core and produce radiant energy.

The huge mass of the Sun produces tremendous pressure and high temperatures deep in its dense interior. Here, the Sun’s abundant hydrogen atoms are forced together and enormous quantities of energy are liberated in the process of fusion. The Sun converts 4.26 million metric tons of mass to heat and light energy every second!

In addition to light and heat, the Sun constantly emits clouds of electrically charged particles. This stream of solar wind travels at about 50 million kilometers (31 million miles) a day, taking approximately 3 days to reach Earth.

The Sun’s most conspicuous features are large sunspots, caused by magnetic storms on the Sun (▶ Fig. 1.3). The number of sunspots is related to the level of activity of the Sun—slightly more energy is radiated when there are more sunspots than when there are fewer sunspots. Individual sunspots may range in diameter from 10,000 to 160,000 km (6200 to 100,000 mi), more than 12 times Earth’s diameter. The eruption in Figure 1.3a was 20 times the diameter of Earth. These produce flares and outbursts of charged material, referred to as coronal mass ejections, that affect radio and satellite communications.

A regular cycle exists for sunspot occurrences, as the number of sunspots increases and decreases, averaging 11 years from maximum to maximum. However, the cycle may vary from 7 to 17 years, with a minimum in 2009 and a maximum in 2014. (For more on the sunspot cycle, see http://solarscience.msfc.nasa .gov/SunspotCycle.shtml; for the latest space weather, see http:// www.spaceweather.com/.)

The massive, glowing ball of gases we call the Sun con- tinuously gives off radiant energy in all directions. The

portion of that energy that reaches Earth provides energy for processes involving the planet’s atmosphere, oceans, and land surface.

Key Learning Concepts ▶ Describe the Sun’s operation, including solar wind.

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1 Solar Energy, Seasons, & the Atmosphere 7

Relative size of Earth

(a) Solar eruption, December 31, 2012

(b) Sunspot maximum in 2000 and minimum in 2009

Oxygen produces green or brownish-red light.

Nitrogen produces blue or red light.

(a) Aurora australis as seen from orbit. (a) Aurora australis as seen from orbit.

(b) Aurora borealis over Whitehorse, Yukon Canada. On August 31, 2012, a coronal mass ejection erupted from the Sun into space, traveling at over 900 miles per second, causing this aurora four days later.

Auroras The charged particles of the solar wind first interact with the magneto- sphere, Earth’s magnetic field, as they approach Earth. The magnetosphere is generated by the motions of Earth’s molten iron outer core. The magne- tosphere deflects the solar wind toward both of Earth’s poles so that only a small portion of it enters the upper atmosphere.

This interaction of the solar wind and the upper layers of Earth’s at- mosphere produces the remarkable auroras that occur toward both poles (▼ Fig. 1.4). These lighting effects are the aurora borealis (northern lights) and aurora australis (southern lights) in the upper atmosphere, 80–500 km (50–300 mi) above Earth’s surface. They appear as folded sheets of green, yellow, blue, and red light that ripple across the skies of higher latitudes, especially poleward of 50°. The different colors of the aurora are due to different molecules in the atmosphere being excited—oxygen produces green or brownish-red light and nitrogen produces blue or red light. During a period in 2001 when the solar wind was stronger than usual auroras were visible as far south as Jamaica, Texas, and California.

▲ 1.4 Auroras from orbit and from the ground

What causes the auroras?geoCheCk✔

Animation Formation of the

Solar System

http://goo.gl/aIti7U

1. How much of the mass of our solar system is the Sun? 2. Why is the Sun the only object in our solar system producing

heat and light? 3. Why are auroras different colors?

geoQuiz

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8 What is the origin & structure of our solar system?

Key Learning Concepts ▶ Explain the characteristics of the electromagnetic spectrum of radiant energy.

1.3 Electromagnetic Spectrum

Wavelength in micrometers (µm) Wavelength in micrometers (µm)

Medical X-rays

Energy discharges from atomic nuclei

Visible light

10–410–8 0.01(10–2) 0.40 0.70 1.50 3.00

Gamma rays X-rays Ultra-violet Near

infrared Shortwave

infrared Visible

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Visible light

Shorter wavelengths Higher frequency

Human body at 37°C (98.6°F) AM radio

Television FM radioMicrowave radarHeat lamp

3.00 5.50 103 (1 mm) 104 106 (1 m)

Middle infrared

Thermal infrared

Microwave Radio waves

Longer wavelengths Lower frequency

▲ 1.5 Electromagnetic spectrum

The essential input of energy to Earth is radiant energy from the Sun. This radiant energy travels to Earth at the speed

of light. Solar radiation occupies a portion of the electro- magnetic spectrum, which is the spectrum of all possible wavelengths of electromagnetic energy (▼ Fig. 1.5). Light can be measured by both its wavelength and frequency. A wavelength is the distance between corresponding points on any two suc- cessive waves. The number of waves passing a fixed point in 1 second is the frequency, thus the shorter the wavelength, the higher the frequency.

Comparing Earth & Sun as Radiating Bodies All objects radiate energy in wavelengths related to their surface tem- peratures: A hotter object emits more energy, with shorter wavelengths, than a cooler object. This holds true for the Sun and Earth. The hotter

Sun radiates shorter-wavelength energy than does Earth, with the Sun’s emissions concentrated around 0.5 μm (micrometer) (▶ Fig. 1.6). The Sun emits radiant energy composed of 8% ultraviolet, X-ray, and gamma-ray wave- lengths; 47% visible light wavelengths; and 45% infrared wavelengths. Ultraviolet energy, because of its shorter wavelength, is higher energy than longer wavelength infrared energy. This is why ultraviolet energy that reaches the surface causes sunburn, skin cancer, and damages the eyesight of human beings, while we perceive infrared energy as heat.

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1 Solar Energy, Seasons, & the Atmosphere 9

The Sun’s surface temperature is about 6000 K (6273°C or 11,459°F). Shorter wavelength emissions are dominant at these higher temperatures.

Earth radiates nearly all of the energy that it absorbs. Because Earth is cooler, it emits less energy and at longer wavelengths, mostly in the infrared portion of the spectrum, centered around 10.0 μm. The smooth curves on the graph in Figure 1.6 represent the radiation emitted by the Sun and Earth. While the curves are smooth, notice that there are gaps at certain wavelengths for actual outgoing radia- tion. These are due to water vapor, water, carbon dioxide, oxygen, ozone (O3), and other gases in Earth’s atmosphere absorbing these wavelengths.

Wavelength in micrometers (µm) Wavelength in micrometers (µm)

Medical X-rays

Energy discharges from atomic nuclei

Visible light

10–410–8 0.01(10–2) 0.40 0.70 1.50 3.00

Gamma rays X-rays Ultra-violet Near

infrared Shortwave

infrared Visible

V io

le t

B lu

G re

Y el

lo w

O ra

n g

R ed

Visible light

Shorter wavelengths Higher frequency

Human body at 37°C (98.6°F) AM radio

Television FM radioMicrowave radarHeat lamp

3.00 5.50 103 (1 mm) 104 106 (1 m)

Middle infrared

Thermal infrared

Microwave Radio waves

Longer wavelengths Lower frequency

150.50.40.20.1

150

Absorbed by CO2 and water vapor

At Earth’s surface

Infrared (45%) Visible (47%)

Ultraviolet (8%)

1051 20.7

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d e

m is

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n s—

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atts p er m

2 p er µ

Wavelength (micrometers, µm)

Absorbed by ozone

At top of atmosphere

At top of Earth’s atmosphere

At Earth’s surface

Absorbed by CO2 and water vapor

▲ 1.6 Solar and terrestrial energy distribution by wavelength The left hand side of the figure shows the distribution of energy from the Sun that reaches the top of our atmosphere (purple line) and Earth’s surface (yellow curve). The right hand side of the figure shows the distribution of energy from Earth out to space as measured at the surface (white line) and at the top of the atmosphere (orange curve).

Why does the Sun emit shorter wavelengths than Earth?geoCHECK✔

geoQUIZ

1. What is the relationship between wavelength and frequency? 2. How does the range of visible wavelengths compare to the range

of energy emitted by the Sun? 3. Which range of wavelengths accounts for most of the energy we

receive from the Sun?

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10 What is the origin & structure of our solar system?

Key Learning Concepts ▶ Describe the global pattern of net radiation.

1.4 Incoming Energy & Net Radiation

How much insolation passes through the top of the atmosphere, but doesn’t reach the surface?

geoCHECK✔

How much solar energy reaches Earth and how is it distributed? The answer to these questions involves

a number of factors, including Earth’s atmosphere, curved shape, and tilted axis. The region at the top of the atmosphere, approximately 480 km (300 mi) above Earth’s surface, is the outer boundary of Earth’s energy system. This is where we study arriving solar radiation before it interacts with the atmosphere.

Because of its distance from the Sun, Earth intercepts only one 1/2,000,000,000 of the Sun’s total energy out- put. This tiny fraction of the Sun’s energy is still an enor- mous amount of energy that flows into Earth’s systems.

Insolation & the Solar Constant Solar radiation arriving at Earth’s atmosphere and surface is insolation, derived from the words “incoming solar radiation” (▶ Fig. 1.7). The solar constant is the average insolation received at the thermopause when Earth is at its average distance from the Sun, a value of 1362 watts per square meter (W/m2). Less than half of the insolation

OUTPUT Longwave radiation

Earth to space

• ultraviolet • visible - main input is light • shortwave infrared

Earth

INPUT Shortwave radiation

Sun to Earth

• thermal infrared - heat

▲ 1.7 Earth’s energy budget Light comes in to Earth from the Sun, Earth radiates heat back to space.

More diffuse, larger area covered

Surface area receiving insolation

The Sun’s parallel rays hit Earth’s surface at oblique angles

Sun’s rays arrive parallel to each other at Earth’s surface

Oblique

Direct

Annually 2.5 times more energy than poles

More concentrated, smaller area

covered

More diffuse

Tropic of Capricorn 23.5° S

Tropic of Cancer 23.5° N

Equator 0°

Location of subsolar point moves between 23.5° N and 23.5° S during the year

Uneven Distribution of Insolation Because Earth’s surface is curved, the angle of incoming sunlight is different at each latitude. Dif- ferences in the angle of sunlight by latitude result in an uneven distribution of insolation and heating. The Sun is directly over the subsolar point, the only location that receives “direct” sunlight, meaning rays of sunlight that strike the surface vertically, at a 90° angle. The subsolar point moves back and forth between the Tropic of Cancer at 23.5° north to the Tropic of Cancer at 23.5° south during the year. In- coming energy is more concentrated in this region, the tropics. All other places away from the subsolar point receive insolation at an angle less than 90° and receive less concentrated energy (◀ Fig. 1.8). This effect is greater at higher latitudes. These higher latitude regions receive less insolation, mainly be- cause of the lower angle of the Sun, but the insola- tion also travels through a greater thickness of the atmosphere. This results in less energy reaching the ground due to scattering, absorption, and reflection in the atmosphere. Because of these factors, the trop- ics receive 2.5 times more energy than the poles.

▲ 1.8 Insolation and Earth’s curved surface

that passes through the top of the atmosphere reaches the surface. The rest is reflected, scattered, and absorbed by the atmosphere.

Why does insolation intensity vary with latitude?

geoCHECK✔

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1 Solar Energy, Seasons, & the Atmosphere 11

Global Net Radiation The difference between incoming shortwave and outgoing long- wave radiation—energy inputs minus energy outputs—is called net radiation. The pattern of net radiation changes with latitude. Satel- lites measured shortwave and longwave flows of energy at the top of the atmosphere to produce the map in Figure 1.9, which shows a latitudinal imbalance in net radiation.

The tropics are a region of positive net radiation values, and the poles are regions of negative values. In middle and high lati- tudes, approximately poleward of 36° north and south, net radia- tion is negative. Negative values occur in higher latitudes because Earth’s climate system loses more energy to space than it gains from the Sun. In the lower atmosphere, energy flows as wind and warm ocean currents from tropical surpluses to the polar energy deficits. The highest net radiation values, averaging 80 W/m2, are above the tropical oceans along a narrow equatorial zone. Net radiation minimums are lowest over Antarctica.

The Sahara region of North Africa is surprisingly a region of net energy loss. Light-colored reflective surfaces, such as fresh snow, and desert sand reduce the absorption of incoming energy, and clear skies allow great amounts of longwave radiation to escape to space. In other regions, clouds and atmospheric

OUTPUT Longwave radiation

Earth to space

• ultraviolet • visible - main input is light • shortwave infrared

Earth

INPUT Shortwave radiation

Sun to Earth

• thermal infrared - heat

▲ 1.7 Earth’s energy budget Light comes in to Earth from the Sun, Earth radiates heat back to space.

< -100 -100 to -80 -80 to -60 -60 to -40 -40 to -20 -20 to 0 0 to 20 20 to 40 40 to 60 60 to 80 >80

ATLANTIC

OCEAN

P A C I F I C

O C E A N

P A C I F I C

O C E A N

I N D I A N

O C E A N

ARCTIC OCEAN

80 70

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0 -20

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80 H 88.3

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0 1500

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3000 KILOMETERS

ROBINSON PROJECTION

Negative values (more energy going out to space than is coming in from the Sun) toward the poles.

Positive values (more energy coming in from the Sun than going out to space) toward the equator and tropics.

Which region has the highest energy surplus?geoCHECK✔

▲ 1.9 Daily net radiation patterns Average daily net radiation flows at the top of the atmosphere. Units are W/m2.

geoQUIZ

1. What is the subsolar point? Where does it migrate during the year? 2. How does the amount of insolation in the tropics compare to the

amount of insolation received at the poles? 3. How do the poles maintain a negative energy balance? More energy

flows out from the poles than comes in from the Sun. Where does that extra energy come from?

pollution in the lower atmosphere affect net radiation patterns at the top of the atmosphere by reflecting more shortwave energy to space.

Having examined the flow of solar energy to Earth and the top of the atmosphere, let us now look at how seasonal changes affect the distribution of insolation as Earth orbits the Sun during the year.

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1.5 The Seasons Key Learning Concepts ▶ Define solar altitude, solar declination, and day length. ▶ Describe the annual variability that produces Earth’s seasonality.

Why do we have seasons?

0°

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December January

February

▲ 1.11 The analemma

If you have lived in one place for a full year, you may have noticed the changes in weather from summer to winter.

You might have also noticed the changes in the length of the day and the angle of the Sun above the horizon. Physical geographers define the seasons in terms of Earth’s changing relationship to the Sun.

Seasonality The changes in the angle of the Sun above the horizon and changes in the hours of daylight are referred to as seasonality. The angle of the Sun above the horizon is the Sun’s altitude. If the Sun is at the horizon, its altitude is 0°. If the Sun is halfway between the horizon and directly overhead, it is at 45° altitude. If the Sun is directly overhead, it is at 90° altitude. The Sun is directly overhead only at the subsolar point, where insolation is at a maximum.

The Sun’s declination is the latitude of the subsolar point (▼ Fig. 1.10). Declination annually migrates between the Tropic of Cancer and Tropic of Capricorn, for a total of 47° of movement. If you marked the location of the Sun in the sky at noon each day throughout the year, you would find that the Sun takes a figure-8 shaped path called an analemma. On the ana- lemma chart in Figure 1.11 you can locate any date, then trace horizontal- ly to the y-axis and find the subsolar point. Along the Tropic of Capricorn, the subsolar point occurs on December 21–22, at the lower end of the analemma. Following the chart, you see that by March 20–21, the subsolar point reaches the equator, and then moves on to the Tropic

of Cancer in June. As an example, use the chart to calculate the subsolar point location on your birthday. Other than Hawaii, the subsolar point does not reach the continental United States or Canada, because these locations are too far north.

Seasonality also produces changes in day length. Day length varies during the year, and the higher the latitude, the larger the difference between summer and winter day lengths. The equator always receives equal hours of day and night, while the poles experience a 24-hour difference in day length. Along the equator every day and night is 12 hours long, year-round. People living along 40° N (Philadelphia, Denver) or 40° S (Buenos Aires, Melbourne) experience about 6 hours’ difference in daylight between winter (9 hours) and summer (15 hours). At 50° N lati- tude (Winnipeg, Paris) or 50° S (Falkland Islands), people experience almost 8 hours of annual day length variation.

How much does day length vary at the equator over a year? At latitude 40° N?

geoCHECK✔

The angle of the Sun above the horizon is the Sun’s altitude.

The latitude of the subsolar point is the Sun’s declination.

On the June solstice, the angle of the Sun above the horizon at 23.5° S is 43°

On the December solstice, the subsolar point is at 23.5°

On the June solstice, the angle of the Sun above the horizon at 23.5° N is 90°

On the June solstice, the subsolar point is at 23.5° N

On the equinoxes, the subsolar point is at 0°

On the solstices, the Sun's angle above the horizon at 0° is 66.5°

▲ 1.10 The Sun’s altitude and declination

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1 Solar Energy, Seasons, & the Atmosphere 13

Reasons for Seasons As Earth revolves around the Sun, a voyage that takes 1 year, it rotates daily around its axis, an imaginary line that goes from the North Pole to the South Pole. Seasonality is created by Earth’s revolution around the Sun, its daily rotation, the tilt of its axis, the orientation of its axis, and its sphericity.

Revolution and Rotation Earth travels at an average speed of 107,280 kmph (66,660 mph) as it revolves around the Sun. Earth orbits the Sun every 365.24 days (▼ Fig. 1.12).

Earth’s rotation, or turning on its axis, averages slightly less than 24 hours in duration. Rotation determines day length, creates the apparent deflection of winds and ocean currents due to the Coriolis effect (see Chapter 4). Rotation

Revolutio n

Sun

Orbit

Plane ofecliptic

Eq u

ator

Eq u

ator

66.5°

23.5°Perpendicular to plane of ecliptic

North PoleNorth Pole

Sun Subsolar point is the Tropic of Cancer

Arctic Circle is 23.5° away from North Pole

Tropics are 23.5° away from Equator

Antarctic Circle is 23.5° away from South Pole

Axis points at North Star

Subsolar point is the Tropic of Capricorn

23.5°

Circle of illumination

Summer Winter

23.5°

Arctic Circle Tropic of Cancer

Tropic of Capricorn

Antarctic Circle

Equator

Arctic Circle Tropic of Cancer

Tropic of Capricorn

Antarctic Circle

Equator

also produces the twice-daily rise and fall of the ocean tides with the gravitational pull of the Sun and the Moon. Viewed from above the equator, Earth rotates west to east, or eastward. This eastward rotation creates the Sun’s apparent westward daily journey from sunrise in the east to sunset in the west. Of course, the Sun actually remains a relatively fixed position in the center of the solar system as our solar system travels through space.

Earth’s rotation produces the daily pattern of day and night. The dividing line between day and night is the circle of illumination (▼ Fig. 1.13).

Axial Tilt and Axial Parallelism Figure 1.13 also shows Earth’s axial tilt. The plane of Earth’s orbit around the Sun is the plane of the ecliptic. Earth’s axis is tilted about 23.5° from perpendicular, but it re- mains fixed relative to this plane as Earth revolves around the Sun. The northern end of the axis points to Polaris, also called the North Star. If Earth orbited the Sun without axial tilt, the equator would always be the subsolar point and all other locations would receive insolation at less than a 90° angle. Earth’s axial tilt of 23.5° determines the locations of the tropics, and the Arctic and Antarctic Circles. The tropics are located 23.5° away from the Equator, at the northern and southern limits of the subsolar point’s annual migration. The Arctic and Antarctic Circles are located 23.5° away from poles at 90° at 66.5°. Every location between the tropics receives sunlight at a 90° angle at some point during the year, while locations north of the Arctic Circle and south of the Antarctic Circle experience 24 hours of daylight and darkness. Through- out our annual journey around the Sun, Earth’s axis points to Polaris and also keeps the same tilt relative to the plane of the ecliptic. If we compared the axis in different months, it would always appear parallel to itself, a condition known as axial parallelism (▼ Fig. 1.13).

Sphericity Because Earth’s surface is curved, different latitudes receive sunlight at different angles on the same day (Fig. 1.8). If Earth wasn’t spherical, sunlight would shine on all locations at the same angle.

What are the five reasons for the seasons?geoCHECK✔

▲ 1.12 Earth’s revolution, rotation, and axial tilt

▲ 1.13 Earth’s circle of illumination

M01_CHRI4744_01_SE_C01.indd 13 23/01/16 1:57 PM

14 Why do we have seasons?

1.5 The Seasons (cont’d)

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View from above the North Pole

North Pole

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Tropic of Cancer

Arctic Circle

Tropic of Capricorn Antarctic Circle

• March 20 or 21. Vernal equinox, or March equinox • Subsolar point is the equator • The circle of illumination passes through both poles • All locations have a 12-hour day • Northern hemisphere

• June 20 or 21, Summer solstice, or June solstice • Subsolar point is the Tropic of Cancer at 23.5° N latitude • North of the Arctic Circle at 66.5° N 24 hours of day light. South of the Antarctic Circle 24 hours of darkness. • Northern hemisphere

• September 22 or 23, Autumnal equinox, or September equinox • Subsolar point is the equator • The circle of illumination passes through both poles • All locations have a 12-hour day • Northern hemisphere

Circle of illumination

Side view Summer (June) solstice

23.5° S

Equator

Tropic of Cancer

Arctic Circle

Tropic of Capricorn Antarctic Circle

• December 21 or 22, Winter solstice or December solstice • Subsolar point is the Tropic of Capricorn at 23.5° S • North of the Arctic Circle at 66.5° N 24 hours of darkness.

South of the Antarctic Circle 24 hours of day light

Side view Winter (December) solstice

June Solstice

December Solstice

March Equinox

September Equinox

March of the Seasons During the annual cycle, or “march,” of the seasons on Earth, day length is the most obvious change for latitudes away from the equator (▶ Fig. 1.14). The extremes of day length occur on the solstices in December and June. The solstices occur when the subsolar point is at its position farthest north at the Tropic of Cancer or farthest south at the Tropic of Capricorn. During the December solstice, the subsolar point is the Tropic of Capricorn and locations above the Arctic Circle experience a 24-hour day, and loca- tions south of the Antarctic Circle a 24-hour night. These day lengths are reversed during the June solstice, when the subsolar point is the Tropic of Cancer. In the Northern Hemisphere, the December solstice marks the beginning of winter, and is called the winter solstice. The winter solstice is also the mid- point of the low sun season. The June solstice marks the beginning of summer, and is called the summer solstice. The summer solstice is also the midpoint of the high sun season. In the Southern Hemisphere the June solstice is the winter solstice and the December solstice is the Summer solstice.

Between the solstices are the equinoxes, when the subsolar point is directly over the equator and day length is 12 hours at all lati- tudes. The September equinox, or autumnal equinox, marks the beginning of autumn in the Northern Hemisphere. The March equi- nox, or vernal equinox, marks the beginning of spring in the Northern Hemisphere.

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View from above the North Pole

North Pole

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View from above the North Pole

Circle of illumination

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23.5°N 23.5°NN

Equator

Tropic of Cancer

Arctic Circle

Tropic of Capricorn Antarctic Circle

Circle of illumination

Side view Summer (June) solstice

23.5° S

Equator

Tropic of Cancer

Arctic Circle

Tropic of Capricorn Antarctic Circle

• December 21 or 22, Winter solstice or December solstice • Subsolar point is the Tropic of Capricorn at 23.5° S • North of the Arctic Circle at 66.5° N 24 hours of darkness.

South of the Antarctic Circle 24 hours of day light

Side view Winter (December) solstice

June Solstice

December Solstice

March Equinox

September Equinox

▲ 1.14 Annual march of the seasons

Animation Earth Sun Relations

http://goo.gl/XVJd3y

M01_CHRI4744_01_SE_C01.indd 14 27/01/16 5:14 pm

1 Solar Energy, Seasons, & the Atmosphere 15

Seasonal Observations The altitude of the Sun changes con- tinuously through the year. In summer, the Sun is higher above the horizon at noon, and in winter, it is closer to the horizon. For example, the Sun’s altitude at local noon at 40° N increases from a 26.5° angle above the horizon at the winter (December) solstice to a 73.5° angle above the horizon at the summer (June) solstice—a range of 47° (▲ Fig. 1.15).

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North Pole

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Circle of illumination

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Tropic of Cancer

Arctic Circle

Tropic of Capricorn Antarctic Circle

Circle of illumination

Side view Summer (June) solstice

23.5° S

Equator

Tropic of Cancer

Arctic Circle

Tropic of Capricorn Antarctic Circle

• December 21 or 22, Winter solstice or December solstice • Subsolar point is the Tropic of Capricorn at 23.5° S • North of the Arctic Circle at 66.5° N 24 hours of darkness.

South of the Antarctic Circle 24 hours of day light

Side view Winter (December) solstice

June Solstice

December Solstice

March Equinox

September Equinox

SunsetSunrise Noon

Winter solstice 26.5°

Summer solstice 73.5°

▲ 1.15 Seasonal observations of the sun—sunrise, noon, and sunset through the year The pale lines in this image are time-lapse photographs of the Sun’s path each day, combined to show how the path changes with the seasons. In the Northern Hemisphere, the Sun’s daily path gradually rises from its lowest on the December solstice to its highest on the June solstice.

Where is the subsolar point on each of the solstices and equinoxes?

geoCHECK✔

1. Why is axial parallelism a crucial part of seasonal changes? 2. How much does the Sun’s altitude vary from the summer solstice to the

winter solstice? 3. Where would the Tropics and Arctic and Antarctic Circles be if Earth’s

axial tilt was 30°?

geoQUIZ

M01_CHRI4744_01_SE_C01.indd 15 23/01/16 1:58 PM

Earth’s atmosphere is a unique mixture of gases that is the product of 4.6 billion years of development, including

the life processes of living organisms. The atmosphere pro- tects us by filtering out harmful radiation and particles from the Sun and beyond. The atmosphere is mainly composed of air. Air is a mixture of gases that is odorless, colorless, taste- less, and blended so thoroughly that it behaves as if it were a single gas.

The top of our atmosphere is around 480 km (300 mi) above Earth’s surface. Beyond that altitude is the exosphere, which means “outer sphere,” where the atmosphere is nearly a vacuum. The exosphere contains scarce lightweight hydrogen and helium atoms, weakly bound by gravity as far as 32,000 km (20,000 mi) from Earth.

Atmospheric Profile If you look at a profile, or cross section, of the atmosphere, you will see that its characteristics change between the surface and the upper atmosphere. Some of these changes reflect the proper- ties of the gases that compose the atmosphere. Other changes reflect the physical properties of the atmosphere itself, such as temperature, pressure, density, and the effects of the force of gravity. The atmosphere’s chemical and physical characteristics produce its layered structure, shown in

Figure 1.16. Gravity compresses air, mak-

ing it denser near Earth’s surface. As you can see in Figure 1.16, the atmosphere thins rapidly with increasing altitude. Air pressure is approximately 1 kg/cm2 (14.7 lb/in.2) at sea level.

At sea level, the atmosphere exerts a pressure of 1013.2 mb (millibar, or mb; a measure of force per square meter of surface area), or 29.92 in. of mercury (symbol, Hg), as measured by a barometer. In Canada and other countries, normal air pressure is expressed as 101.32 kPa (kilopascal; 1 kPa = 10 mb). As you will see, the atmosphere’s com- position and temperature, and the functions of different layers, also vary with altitude.

What are the properties of our atmosphere?

Key Learning Concepts ▶ Draw a diagram showing a profile of atmospheric structure based on

composition.

1.6 Atmospheric Composition

▲ 1.16 Density decreasing with altitude Have you experienced pressure changes that you could feel on your eardrums? How high above sea level were you at the time? The pressure profile plots the decrease in pressure with increasing altitude. Pressure is in millibars and as a percentage of sea level pressure. Note that the troposphere holds about 90% of the atmospheric mass (far-right % column).

Why is air pressure higher closer to the surface?geoCHECK✔

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Hydrogen Helium

Oxygen Nitrogen

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Atmospheric Composition

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Higher density, higher pressure

Lower density, lower pressure

M01_CHRI4744_01_SE_C01.indd 16 23/01/16 1:58 PM

1 Solar Energy, Seasons, & the Atmosphere 17

Atmospheric Gases In terms of chemical composition, the atmosphere has two broad regions, the heterosphere (80–480 km altitude) and the homosphere (Earth’s surface to 80 km altitude). Gases in the homosphere are well mixed, while gases in the heterosphere are layered by density.

Heterosphere The layer of the atmosphere from about 80 km (50 mi) altitude to the exosphere is the heterosphere. Gases in the heterosphere are sorted by gravity into distinct layers based on their density. Oxygen and nitrogen are dominant in the lower hetero- sphere, while the upper portions are made of hydrogen and helium.

Homosphere The layer of the atmosphere from Earth’s surface to an altitude of 80 km (50 mi) is called the homosphere. While air pressure decreases rapidly as you go up through the homosphere, the gases are still well mixed. The ozone layer is the region with

a higher concentration of ozone, from 19 to 40 km (12 to 24 mi). Figure 1.17 shows the amounts of gases in dry, clean air in the homosphere. These gases are considered stable gases, because the proportion of gases does not vary much. CO2 is classified as a stable gas, even though it is increasing, because its concentration varies over time periods of years to tens of thousands of years. Addition- ally, its concentration does not vary much globally. There are also water vapor, pollut-

ants, and some trace chemicals in the lowest portion of the atmos- phere. These are considered variable gases because their amounts vary over short time periods, from hours to weeks. In terms of just the stable gases, the atmosphere is made up of the following:

• 78% relatively inert nitrogen • 21% oxygen. (Oxygen is crucial in life processes on Earth.

Although it forms about one-fifth of the atmosphere, oxygen compounds compose about half of Earth’s crust.)

• Less than 1% argon, which is inert and unusable in life processes • 0.04% (400 parts per million [ppm]) carbon dioxide (CO2)

Carbon dioxide is a natural by-product of life processes. However, atmospheric CO2 has been increasing rapidly, as shown in Figure 1.18. Scientists agree that the increase is anthropogenic, or human caused. You will learn about the role of rising CO2 concen- trations in anthropogenic climate change in Chapter 7.

Carbon Dioxide and Climate Change Carbon dioxide is a green- house gas—that is, a gas that absorbs and emits infrared radiation as heat. While it makes up less than 1% of the gases in the homo- sphere, it is very important in maintaining Earth’s temperature because it delays heat exiting the atmosphere, much like a blanket. Without CO2 in our atmosphere, global temperatures would be below freezing. Nitrogen, oxygen, and the other 99% of the atmos- phere is made up of gases that are not greenhouse gases. Over the past 200 years, the CO2 percentage increased as a result of human activities, principally the burning of fossil fuels and deforestation. According to ice core records, CO2 is higher now than at any time in the past 800,000 years. Since 1959, the global concentration of CO2 in our atmosphere has increased more than 27%, reaching a peak of over 404 ppm in May, 2015 (▼ Fig. 1.18). Today’s CO2 level far exceeds the natural range of 180–300 ppm over the last 800,000 years. If this rate of increase continues for the rest of the century, then then CO2 levels could be 1000 ppm CO2 in 2100.

The rate of increase in CO2 is accelerating. From 1990 to 1999, CO2 emissions rose at an average of 1.1% per year. Compare this to the average emissions increase since 2000 of 3.1% per year. A distinct climatic threshold is approaching at 450 ppm, sometime in the dec- ade of the 2020s. Beyond this tipping point, many scientists believe there would be irreversible consequences, discussed in Chapter 7.

0.040% Carbon dioxide (CO2) 0.934% Argon (Ar)

Trace gases

78.084% Nitrogen (N2)

20.946% Oxygen (O2)

▲ 1.17 Stable components of the atmosphere

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1960 1970 1980 1990 2000 2010 2020

Atmospheric CO2 at Mauna Loa Observatory, Hawai'i

Year

▲ 1.18 Recent changes in carbon dioxide levels Atmospheric CO2 concentrations from 1959 to the present.

What are the main gases in the atmosphere?geoCHECK✔

1. How high would you have to be to have half the atmosphere beneath you?

2. How do current levels of CO2 compare to levels over the last 800,000 years?

geoQUIZ

M01_CHRI4744_01_SE_C01.indd 17 23/01/16 1:58 PM

1.7 Atmospheric Temperature Key Learning Concepts ▶ Draw a diagram showing a profile of atmospheric structure based on its

temperature.

What are the properties of our atmosphere?

Based on temperature, the atmosphere has four distinct temperature zones—

the thermosphere, mesosphere, strato- sphere, and troposphere (▶ Fig. 1.19).

Thermosphere The thermosphere (“heat sphere”) roughly corresponds to the heterosphere. The thermo- sphere is a region of very low air pressure, few molecules, and high temperatures. An oxygen molecule in the thermosphere can travel a kilo- meter before colliding with another molecule.

Intense solar radiation in this portion of the atmosphere excites individual molecules to high levels of vibration. The temperature profile in Figure 1.19 (yellow curve) shows that tempera- tures rise sharply in the thermosphere, to 1200°C (2200°F) and higher. Despite such high tempera- tures, the thermosphere is not “hot” in the way you might expect, because temperature and heat are different concepts. Heat is energy, temperature is a measure of energy. Temperature is a measure of kinetic energy, the energy of motion. Heat is the flow of kinetic energy from one body to another, and depends on density. The actual heat in the thermosphere is small because there are so few molecules. Heating increases near Earth’s surface because the greater number of molecules in the denser atmosphere transmits their kinetic energy as sensible heat, meaning that we can measure and feel it.

Mesosphere The mesosphere is the area from 50 to 80 km (30 to 50 mi) above Earth and is within the homosphere. At high latitudes, an observer at night may see bands of ice crystals glow in rare and unusual noctilucent clouds, which are so high in altitude that they still catch sun- light after the Sun has set below the horizon.

Thermosphere

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Equatorial tropopause

Polar tropopausePolar tropopause Troposphere

Stratosphere

Temperature decreases with increased altitude through the troposphere at the normal lapse rate of 6.4C° per kilometer (3.5F° per 1000 ft).

How are temperature and heat different?

geoCHECK✔

▲ 1.19 Temperature profile of the atmosphere

Based on Figure 1.19, what is the temperature range of the mesosphere?

geoCHECK✔

M01_CHRI4744_01_SE_C01.indd 18 23/01/16 1:58 PM

1 Solar Energy, Seasons, & the Atmosphere 19

Stratosphere The stratosphere extends from 18 to 50 km (11 to 31 mi) from Earth’s surface. Temperatures increase with altitude throughout the stratosphere, from –57°C (–70°F) at 18 km at the stratosphere’s lower limit, warming to 0°C (32°F) at 50 km at the stratosphere’s outer boundary, the stratopause. (The suffix –pause means “to change.”) This warming is caused by ozone converting ultraviolet energy to heat. The ozone layer is the portion of the stratosphere with a higher concentration of ozone. In module 1.8, you will learn how the ozone layer protects living things from ultraviolet radiation, how scientists identified a human- caused threat to the ozone layer, and how nations have worked together to restore the ozone layer.

Figures 1.20 and 1.21 offer two perspectives on the scale of Earth’s atmosphere.

Why do temperatures increase in the stratosphere?

geoCHECK✔

Troposphere The troposphere is the atmospheric layer that supports life and is the region of principal weather activity. Approxi- mately 90% of the total mass of the atmosphere and the bulk of all water vapor, clouds, and air pollution are within the troposphere. An average temperature of –57°C (–70°F) defines the tropopause, the troposphere’s upper limit, but its exact altitude varies with the season, latitude, and surface tem- peratures and pressures. Near the equator, because of intense heating from the surface, the tropopause occurs at 18 km (11 mi); while at the North and South Poles it averages only 8 km (5 mi) or less above Earth’s surface. The marked warm- ing with increasing altitude in the stratosphere above the tropopause causes the tropopause to act like a lid, generally preventing whatever is in the cooler (denser) air below from mixing into the warmer (less dense) stratosphere. As Figure 1.19 shows, temperatures decrease rapidly

How much of the atmosphere’s mass is in the troposphere?geoCHECK✔

geoQUIZ

1. Why wouldn’t you feel hot in the thermosphere, even with a temperature of 1200°C?

2. Why is the tropopause found at different altitudes at different latitudes? Explain. 3. Why do temperatures decrease with increased altitude through the troposphere?

with increasing altitude at an average of 6.4C° per kilometer (3.5F° per 1000 ft), a rate known as the normal lapse rate.

The normal lapse rate is an average. The actual lapse rate, called the environmental lapse rate, may vary considerably because of local weather conditions.

▼ 1.21 The International Space Station (ISS) orbits Earth The ISS travels within the Thermosphere, ranging between 350 m and 430 km above Earth’s surface, with 400 km (249 mi) the ideal altitude.

▲ 1.20 Felix Baumgartner’s 2012 parachute jump from 39 km (24 mi) in the stratosphere

M01_CHRI4744_01_SE_C01.indd 19 23/01/16 1:58 PM

20 What are the properties of our atmosphere?

Key Learning Concepts ▶ Draw a diagram showing a profile of atmospheric structure based on function. ▶ Describe conditions within the stratosphere. ▶ Summarize the function and status of the ozone layer.

1.8 The Atmosphere’s Functional Layers

Ozone layer That portion of the stratosphere that contains an increased level of ozone is the ozone layer. Ozone is a highly reactive oxygen molecule made up of three oxygen atoms (O3) instead of the usual two atoms (O2) that make up oxygen gas. Ozone absorbs ultraviolet energy and radi- ates longer wavelengths of infrared radiation as heat (▼ Fig. 1.23). This process converts most harmful ultraviolet radiation, effectively “filter- ing” it and safeguarding life at Earth’s surface. At its densest, the ozone layer contains only 1 part ozone per 4 million parts of air. The ozone layer would be only 3 mm thick if it were compressed to surface pressure.

The ozone layer has been relatively stable over the past several hundred million years. Today, however, it is in a state of continuous change because of anthropogenic, or human- caused, pollutants.

The atmosphere has two specific functional zones, the ionosphere and the ozone layer (also called the ozonosphere), which remove

most of the harmful wavelengths of incoming solar radiation and charged particles. Figure 1.22 shows where radiation is absorbed by the functional layers of the atmosphere.

Ionosphere The outer functional layer, the ionosphere, extends throughout the thermosphere and the mesosphere. The ionosphere absorbs cosmic rays, gamma rays, X-rays, and shorter wavelengths of ultraviolet radiation, changing atoms to positively charged ions and giving the ionosphere its name. The glowing auroras occur principally within the ionosphere.

How do we know that the ionosphere is absorbing energy from the Sun?

geoCheCK✔

Ultraviolet light hits a chlorofluorocarbon (CFC) molecule, breaking off a chlorine atom.

Once free, the chlorine atom is off to attack

another ozone molecule.

A free oxygen atom pulls the oxygen atom off the chlorine monoxide molecule.

The chlorine atom and the oxygen atom join to form a chlorine monoxide molecule.

The chlorine atom attacks an ozone molecule, pulling an oxygen atom off it.

Cl C

ClCl

Sun

▲ 1.23 Ozone breakdown by CFCs

Which wavelengths of light does the ozone layer filter?

geoCheCK✔300

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X-rays

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infrared Shortwave

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▲ 1.22 Atmospheric function

Animation The Ozone Layer

http://goo.gl/V8JNt3

M01_CHRI4744_01_SE_C01.indd 20 27/01/16 5:15 pm

1 Solar Energy, Seasons, & the Atmosphere 21

Stratospheric Ozone Losses: A Continuing Health Hazard The area of stratospheric ozone depletion above Antarctica has grown since 1979, with the record depletion in 2006 cov- ering about 30 million square kilometers (▼ Fig. 1.24). Ozone is thinning over the rest of the Southern Hemisphere, as well. In Ushuaia, Argentina, UVB inten- sity is 225% higher than normal.

Increased ultraviolet radia- tion is affecting atmospheric chemistry, biological systems, phytoplankton (small photosynthetic organisms that are largely responsible for the ocean’s primary food pro- duction), fisheries, crop yields, and human skin, eye tissues, and immunity. An international scien- tific consensus confirmed the anthropogenic disruption of the ozone layer.

Ozone Losses Explained Because chlorofluorocar- bons (CFCs) are stable at Earth’s surface and possess remarkable heat properties, they were used in aerosol sprays, as refrigerants, and in the electronics industry. They are inert—they do not dissolve in water and do not break down in biological processes. Tens of millions of tons of CFCs were sold worldwide since 1950 and released into the atmosphere. Chlorine compounds from volcanic eruptions and ocean sprays are water soluble and rarely reach the stratosphere.

In 1974, F. Sherwood Rowland and Mario Molina cor- rectly hypothesized that stable molecules move into the stratosphere, where they are split apart by ultraviolet radia- tion, freeing chlorine (Cl) atoms. This process breaks up ozone molecules (O3) and leaves oxygen molecules (O2) in their place (Fig 1.21). Each chlorine atom can break down more than 100,000 ozone molecules, partially because they can stay there for 40 to 100 years.

Ozone loss is highest over Antarctica because of the com- bination of thin, icy clouds in the stratosphere and Antarctic wind patterns. Depletion of ozone develops in the Antarctic spring and usually peaks in September. Over the North Pole, conditions are more changeable, so the hole is smaller, al- though growing each year, with a new record set in 2011.

An International Response As the science around depletion of the ozone layer became established, sales and production of CFCs declined. During this period, however, chemical manufacturers claimed that no evidence existed to prove the ozone-depletion model, and they successfully delayed remedial action from 1974 until 1987. To make matters worse, a March 1981 presidential order permitted the export and sales of banned prod-

ucts. Sales increased and hit a new peak in 1987 at 1.2 million metric tons (1.32 million tons).

Finally, in 1987, an internation- al agreement went into effect

halting further sales growth. The Montreal Protocol on Substances That Deplete

the Ozone Layer aims to reduce and eliminate CFC damage to the ozone layer. With 189 signatory coun- tries, the protocol is regarded as probably

the most successful international agreement

in history. Today, with exten-

sive scientific evidence and verification of ozone losses, even

the CFC manufacturers admit that the problem of ozone depletion is serious. Thanks to the Montreal Protocol, CFC sales continue their decline, and scientists estimate that the stratosphere will return to more

normal conditions in a century if the protocol is enforced. Developing countries have been allowed to delay the end of production and use of CFCs. Recovery is proceeding slower than previously thought, despite the slowing rate of accumulation of offending chemicals.

Without this treaty the ozone layer could have disappeared by 2100, causing several million more cases of skin cancer. For their work, Row- land, Molina, and another colleague, Paul Crutzen, received the 1995 Nobel Prize for Chemistry. The Royal Swedish Academy of Sciences said “the three researchers have contributed to our salvation from a global environmental problem that could have catastrophic consequences.” See http://ozonewatch.gsfc.nasa.gov/, and http://www.ec.gc.ca/ozone/ to see how our stratosphere is doing.

▲ 1.24 The Antarctic ozone hole Images show the size of the ozone “hole” in 1980 and 2011. Blues and purples show low ozone; greens, yellows, and reds show high ozone.

When and where did the ozone hole reach maximum size? Explain.

geoCHECK✔

geoQUIZ

1. How do CFCs break down ozone? 2. Would the ozone layer have repaired itself without the Montreal Protocol?

Explain.

September 1980 September 2011

Ozone (Dobson units) 110 220 330 440 550

Video The Ozone Hole

http://goo.gl/Z9LsBX

M01_CHRI4744_01_SE_C01.indd 21 25/01/16 12:25 PM

22 What are the properties of our atmosphere?

Key Learning Concepts ▶ Distinguish between natural and anthropogenic pollutants in the lower

atmosphere.

1.9 Variable Atmospheric Components

Natural and anthropo- genic pollutants in the

troposphere are important topics of research in physi- cal geography because they have serious human-health implications. Pollutants are gases, particles, and other chemicals in the atmosphere that are harmful to human health or cause environmen- tal damage. Air pollution is not a new problem. Romans complained more than 2000 years ago about the stench of open sewers, smoke from fires, and fumes from kilns and furnaces that converted ores into metals. Air pollution has historically occurred around cities and is closely linked to hu- man production and consumption of energy and resources.

Because pollution moves across political borders and oceans, solutions require regional, national, and international strategies. Regulations to curb human-caused air pollution have achieved great success, although much remains to be done. Before we discuss these topics, let’s examine some natural pollution sources (▲ Fig. 1.25).

Natural Sources of Air Pollution Natural air pollution sources, such as wildfires and volcanoes, produce a greater volume of pollutants than do human-made sources. However, any attempt to dismiss the impact of human-made air pollution by comparing it with natural sources is misguided, for we did not evolve with anthropogenic (human-caused) contaminants.

A dramatic natural source of pollution was the 1991 eruption of Mount Pinatubo in the Philippines, perhaps the 20th century’s second largest eruption. This event injected nearly 20 million tons of sulfur dioxide (SO2) into the stratosphere.

Devastating annual wildfires on several continents produce natural air pollution (▶ Fig. 1.26). Wildfire smoke contains particulate matter (dust, smoke, soot, ash), nitrogen oxides, carbon monoxide, and volatile organic compounds that darken skies and damage health. Scientists related increas- ing wildfires in the western United States to climate change: Higher spring and summer temperatures and earlier snowmelt are extending the wildfire season and increasing the intensity of wildfires in the western United States: “large wildfire activity increased suddenly and markedly in the mid-1980s, with higher large-wildfire frequency, longer wildfire durations, and longer wildfire seasons.”*

▲ 1.25 Downwind from a volcano (a) Ash from the April 2010 eruption of Eyjafjallajökull was blown south by the jet stream, (b) disrupting international air travel.

What are some of the reasons for increased annual wildfires in the American West?

geoCHECK✔

*A. L. Westerling et al., “Warming and earlier spring increase western U.S. forest wildfire activity,” Science 313, 5789 (Aug. 18, 2006): 940.

These connections occur across the globe, as in drought- plagued Australia or the 2015 record wildfires in Canada, Alaska, and California. Each year, worldwide, wildfire acreage breaks the record of the previous year.

(b)(a)

▲ 1.26 Smoke from California wildfires The main fire in this image is the Rim Fire, which burned more than 257,000 acres (104,000 hectares) from August 17, 2013 to October 24, 2013.

M01_CHRI4744_01_SE_C01.indd 22 23/01/16 1:58 PM

1 Solar Energy, Seasons, & the Atmosphere 23

In cr

ea si

n g

a lt

it u

d e

Decreasing temperature

6.4 C°/1000 m

3.5 F°/1000 ft

Decreasing temperature

In cr

ea si

n g

a lt

it u

d e Warmer air

Inversion layer

Mixing in the

atmosphere

Mixing blocked— pollution trapped beneath inversion

Inversion layer

(a) A normal temperature profile.

(b) A temperature inversion in the lower atmosphere prevents the cooler air below the inversion layer from mixing with air above. Pollution is trapped near the ground.

▲ 1.28 Normal and inverted temperature profiles

Natural Factors That Affect Air Pollution Wind, local and regional landscape charac- teristics, and temperature inversions in the troposphere can increase the problems of air pollution.

Winds Winds transport air pollution from the United States to Canada and Europe. In Europe, the cross-boundary drift of pollution is an issue because of the proximity of coun- tries. Dust from Africa contributes to the soils of South America and Europe, and Texas dust ends up across the Atlantic (▶ Fig. 1.27).

Pollution is carried from industry and fires in the midlatitudes to the Arctic, causing Arctic haze. This was first observed by pilots in the 1950s. Haze is a concentration of microscopic particles and air pollution that diminishes air clarity. Since these high latitudes have few people and lack industry, this haze is the prod- uct of pollutants transported to the Arctic.

Local and Regional Landscapes Local and re- gional landscapes are another important factor in air pollution. Surrounding mountains and hills can trap and concentrate air pollution or direct pollutants from one area to another.

Volcanic landscapes such as Iceland and Hawaii have their own natural pollution. During periods of sustained volcanic activity at Kilauea, some 2000 metric tons (2200 tons) of sulfur dioxide are produced a day, sometimes meriting public health announcements. The resulting acid rain and volcanic smog, called vog by Hawaiians (for vol- canic smog), cause losses to agriculture as well as other economic impacts.

Temperature Inversions A tempera- ture inversion occurs when the tem- perature of the atmosphere increases with altitude, rather than decreasing with altitude at the normal lapse rate (▼ Fig. 1.28). Inversions can result from certain weather conditions, such as cool air blowing in off the ocean, or when the air near the ground is radiatively cooled on clear nights, or from topographic situations that produce cold-air drainage into valleys. A normal temperature profile permits warmer and less dense air at the surface to rise, moderating surface pollu- tion. When an inversion occurs, warm air from the surface rises, but it is trapped by the warmer air of the inversion layer.

Why do we need to look beyond local

control of pollution?

geoCheCk✔

geoQuIz

1. What are some sources of natural air pollution? 2. What are two natural factors that affect air

pollution levels?

Atlantic Ocean

N Cape Verde

Western Sahara

Mauritania

100 KILOMETERS

▲ 1.27 Winds carrying dust in the atmosphere Animation

The Ozone Layer

http://goo.gl/V8JNt3

(b)(a)

▲ 1.26 Smoke from California wildfires The main fire in this image is the Rim Fire, which burned more than 257,000 acres (104,000 hectares) from August 17, 2013 to October 24, 2013.

M01_CHRI4744_01_SE_C01.indd 23 27/01/16 5:15 pm

24 What are the properties of our atmosphere?

Key Learning Concepts ▶ Construct a simple diagram illustrating the pollution from photochemi-

cal reactions in motor vehicle exhaust. ▶ Describe the sources and effects of industrial smog, acid deposition,

and particulates. ▶ Discuss the Clean Air Act’s impact on air pollution.

1.10 Anthropogenic Pollution

A nthropogenic air pollution is more common in ur- banized regions and is responsible for roughly 2% of

annual deaths in the United States, China, India, as well as Canada, Europe, and Mexico (▶ Fig. 1.29). As urban popula- tions grow, human exposure to air pollution increases. In 2012, for the first time, more than 50% of world population lived in metropolitan regions, some one-third with un- healthful levels of air pollution. This is a potentially massive public health issue in this century. For example, asthma rates have nearly doubled since 1980 in the United States due to motor vehicle–related air pollution. Adverse health impacts can result from several types of pollution, including photochemical smog, peroxyacetyl nitrates, industrial smog and sulfur oxides, and particulates.

Photochemical Smog Photochemical smog is formed by sunlight interacting with chemicals in automobile exhaust (▼ Fig. 1.30). Smog is the major component of anthropo- genic air pollution and is responsible for the hazy sky and reduced sunlight in many of our cities.

North American urban areas may have from 10 to 100 times higher nitro- gen dioxide (NO2) concentrations than nonurban areas. Nitrogen dioxide and water vapor form nitric acid (HNO3).

▼ 1.30 Photochemical smog

PANs

Solar radiation

Volatile organic compounds (VOCs) In the environment: Prime agents of surface ozone formation

Peroxyacetyl nitrates (PANs) In the environment: Major damage to plants, forests, crops Health effects: No human health effects

Ozone (O3) Highly reactive, unstable gas In the environment: Damages plants Health effects: Irritates human eyes, nose, and throat

NO + VOC

NO2 (nitrogen dioxide)

(water)

(nitric acid)

CO (carbon

monoxide)

Photochemical smog

Ultraviolet radiation

Acid deposition

H2O

NO2

HNO3

O (atomic oxygen)

O2 (molecular oxygen)

O3 (ozone)

(nitric oxide)

Carbon monoxide (CO) Odorless, colorless, tasteless gas Health effects: Toxic; displaces O2 in bloodstream; 50 to 100 ppm causes headaches and vision and judgment losses

Nitric oxide (NO) molecules react with volatile or- ganic compounds (VOCs) such as the hydrocarbons in gasoline. This reaction produces peroxyacetyl nitrates (PAN), which are particularly damaging to plants, including agricultural crops and forests.

Ozone is the primary ingredient in photochemi- cal smog. The same gas that is beneficial to us in the stratosphere damages biological tissues in the lower atmosphere. Children are at greatest risk from ozone pollution—one in four children in U.S. cities is at risk of developing health problems from ozone pollution. For more information and city rankings, see www .lungusa.org/.

Industrial Smog & Sulfur Oxides Air pollution associated with coal-burning industries is known as industrial smog (▶ Fig. 1.31). Sulfur dioxide (SO2) reacts with oxygen and water to make sulfate aerosols and sulfuric acid (H2SO4). Coal-burning electric utilities and steel manufacturing are the main sources of sulfur dioxide. Sulfur dioxide–laden air is dangerous to health, corrodes metals, and deteriorates stone building materials. Sulfuric acid and nitric acid deposition have increased since the 1970s.

What is the major component of urban air pollution?

geoCHECK✔

▲ 1.29 Air pollution in China

M01_CHRI4744_01_SE_C01.indd 24 23/01/16 1:58 PM

1 Solar Energy, Seasons, & the Atmosphere 25

Acid Deposition Sulfuric and nitric acid deposition is a major environ- mental issue in some areas of the United States, Canada, Europe, and Asia. Such deposition is most familiar as “acid rain,” but it also occurs as “acid snow” and as dust. Normal precipitation is slightly acidic, but acid deposition has been measured at 10 times the acidity of lemon juice! Government estimates of damage from acid deposition in the United States, Canada, and Europe exceed $50 billion annually.

Acid deposition is causally linked to serious environmental prob- lems: declining fish populations and fish kills, widespread forest dam- age, changes in soil chemistry, and damage to buildings and sculptures. Regions that have suffered most are the northeastern United States, southeastern Canada, Sweden, Norway, Germany, much of eastern Europe, and China. Amendments to the Clean Air Act have resulted in a 40% drop in SO2 emissions and a 65% drop in acid rain levels since 1976.

Particulates A mixture of fine particles, both solid and liquid, that impact human health is referred to as particulate matter (PM). Small particles in the air are called aerosols. The smaller the particle, the greater the health risk. These fine particles, such as combustion particles, organ- ics, and metallic aerosols, can get into the lungs and bloodstream. Coarse particle (PM10) particulates smaller than 10 microns (10 μm or less) in diameter, are of less concern, although they can irritate a person’s eyes, nose, and throat. Ultrafines, which are PM0.1, can get into smaller channels in lung tissue and cause scarring, abnormal thickening, and damage called fibrosis.

Effects of the Clean Air Act The Clean Air Act is a U.S. federal law enacted in 1970 and amended in 1977 and 1990. It established national air quality standards and air quality monitoring, automobile emission and fuel economy standards, power plant emission standards, and ozone protection standards. As a result of the Clean Air Act, our air now contains 98% less lead, 45% less carbon monoxide, 22% less nitrogen oxides, 48% less volatile organic

What are the main sources of sulfur dioxide?geoCHECK✔

Which is more harmful—fine aerosols or coarse aerosols? Explain.

geoCHECK✔

How has the Clean Air Act improved air quality and saved money?

geoCHECK✔

geoQUIZ

1. How does PAN form from automobile exhaust? 2. How is PM dangerous to human health?

compounds, 75% less PM10 particulates, 52% less sulfur oxides.

The health benefits of the Clean Air Act have far out- weighed the costs of reducing air pollution. An exhaustive cost–benefit analysis found a 42-to-1 benefit-over-cost ratio! The Environmental Protection Agency (EPA) report calcu- lated that the total direct cost to implement all the Clean Air Act rules from 1970 to 1990 was $523 billion (in 1990 dol- lars). The estimated direct economic benefits had a central mean of $21.2 trillion, making the estimated net financial benefit of the Clean Air Act $21.7 trillion!

In 2010, the Clean Air Act saved society $110 billion, and cost $27 billion. More than 13 million lost workdays,

3 million lost school days, 160,000 adult deaths, 1,700,000 asthma attacks, 130,000 heart attacks, and 86,000 emer- gency room visits were avoided in 2010 alone. Despite this, air pollution regulations have been subjected to continued political attacks.

▲ 1.31 Industrial smog

Nitrogen oxides NOx (NO, NO2) Reddish-brown, choking gas given off by agricultural activities, fertilizers, and gasoline-powered vehicles In the environment: Leads to acid deposition Health effects: In�ames respiratory system, destroys lung tissue

Sulfur oxides (SOx, SO2, SO3) Colorless gas with irritating smell produced by combustion of sulfur-containing fuels In the environment: Leads to acid deposition Health effects: Impairs breathing, causes human asthma, bronchitis, emphysema

Particulate matter (PM) Complex mixture of solids and aerosols, including dust, soot, salt, metals, and organic chemicals In the environment: Dust, smoke, and haze affect visibility Health effects: Causes bronchitis, impairs pulmonary function

Acid deposition

Industrial smog

H2O (water)

HNO3 (nitric acid)

Nitrogen from fertilizers

Particular matter (PM)

Particulates

NO2 NO2 (nitrogen dioxide from combustion)

CO2 SO2

SO2 (sulfur dioxide)

H2SO4 (sulfuric acid)

O2 (oxygen)

H2O (water)

M01_CHRI4744_01_SE_C01.indd 25 23/01/16 1:58 PM

Clean burning cooking stoves will reduce the amount of fine particulates such as black carbon in developing countries. Several international initiatives are working toward this goal (see http://www.projectsurya.org/).

London implemented new low emissions standards for diesel vehicles in 2012. Owners must comply or face a daily penalty fee. Stricter regulation is one strategy to control increasing air pollution from the transportation sector.

As summers get longer in Alaska, moose migrations no longer coincide with the hunting seasons of native people, who depend on the meat. Shifting animal migrations and vegetation patterns will affect ecosystems across the globe.

NASA’s 2012 portrait of global aerosols shows dust lifted from the surface in red, sea salt in blue, smoke from fires in green, and sulfate particles from volcanoes and fossil fuel emissions in white.

1890 –6

–4

–2

1900 1910 1920 1930 1940 1950

Year

Timing of last spring frost and first fall frost 1895–2011

Spring frost

Fall frost

Long-term average

D ev

ia ti

o n

f ro

m a

ve ra

g e

(d ay

1960 1970

Positive values show that frost occurred later in the year

Negative values show that frost occurred earlier in the year

1980 1990 2000 2010 2020

Data for the contiguous United States show an overall trend toward a longer growing season, with a longer fall and an earlier spring.

SEASONS/ATMOSPHERE IMPACTS HUMANS

• Solar energy drives Earth systems. • Seasonal change is the foundation of many human societies; it determines rhythm of life and food resources. • Earth’s atmosphere protects humans by filtering harmful wavelengths of light, such as ultraviolet radiation. • Natural pollution from wildfires, volcanoes, and wind-blown dust are detrimental to human health.

HUMANS IMPACT SEASONS/ATMOSPHERE • Climate change affects timing of the seasons. Changing temperature and rainfall patterns mean spring is coming earlier and fall is starting later. Prolonged summer temperatures heat water bodies and affect seasonal ice cover, alter animal migrations, and shift vegetation patterns to higher latitudes. • Human-made chemicals deplete the ozone layer. Winds concentrate these pollutants over Antarctica, where the ozone hole is largest. • Anthropogenic air pollution collects over urban areas, reaching dangerous levels in some regions, such as northern India and eastern China; other regions have improved air quality, as in the Los Angeles metropolitan area.

ISSUES FOR THE 21ST CENTURY • Ongoing climate change is altering Earth systems. Societies will need to adapt their resource base as timing of seasonal patterns changes. • Human-made emissions must be reduced to improve air quality in Asia. Air pollution will continue to improve in regions where emissions are regulated, such as in Europe, the United States, and Canada. • Alternative, clean energy sources are vital for reducing industrial pollution worldwide. • Fuel efficiency, vehicle-emissions regulations, and alternative and public transportation are crucial for reducing urban pollution and CO2 emissions that drive climate change.

THEhumanDENOMINATOR 1 Seasons & the Atmosphere

Looking Ahead In the next chapter, we follow the flow of energy through the lower portions of the at- mosphere as insolation makes its way to the surface. We establish the Earth–atmosphere energy balance and examine how surface energy budgets are powered by this arrival of energy. We also begin exploring the outputs of the energy–atmosphere system, focus- ing on temperature concepts, temperature controls, and global temperature patterns.

M01_CHRI4744_01_SE_C01.indd 26 23/01/16 1:59 PM

Chapter Review 27 Chapter 1 Review 27

Why do we have seasons?

1.5 The Seasons

Define solar altitude, solar declination, and day length. Describe the annual variability that produces Earth’s seasonality.

• The angle between the Sun and the horizon is the Sun’s alti- tude. The Sun’s declination is the latitude of the subsolar point

• Earth’s seasons are produced by Earth’s axial tilt of about 23.5° from a perpendicular to the plane of the ecliptic, which affects the amount of solar radiation different parts of Earth receive at different times of year.

• December 21 or 22 is the winter solstice in the Northern Hemisphere, or December solstice. The subsolar point is at the Tropic of Capricorn (23.5° S).

• March 20 or 21 is the vernal equinox in the Northern Hemi- sphere, or March equinox. September 22 or 23 is the autumnal, equinox in the Northern Hemisphere or September equinox. On the equinoxes, the subsolar point is over the equator. All locations on Earth experience a 12-hour day and night.

• June 20 or 21 is the summer solstice in the Northern Hemi- sphere, or June solstice. The subsolar point is at the Tropic of Cancer (23.5° N). North of the Arctic Circle there are 24 hours of daylight, while the area from the Antarctic Circle to the South Pole is in darkness.

6. List the five physical factors that operate together to produce seasons.

7. What are the solstices and equinoxes, and what is the Sun’s declination at these times?

What are the properties of our atmosphere?

1.6 Atmospheric Composition

Draw a diagram showing a profile of atmospheric structure based on composition.

• Air is a mix of gases so evenly blended it behaves as if it were a single gas.

• The weight of the atmosphere is air pressure. It decreases rap- idly with altitude.

• By composition, we divide the atmosphere into the homosphere, from Earth’s surface to 80 km, and the heterosphere, from 80 km (50 mi) to 480 km (300 mi). Gases in the homosphere are well mixed, while gases in the heterosphere are sorted by gravity.

• Carbon dioxide levels are higher now than at any other time in the past 800,000 years. Not only is the level of CO2 increasing, but the rate of increase is also increasing.

8. Name the four most prevalent stable gases in the homosphere. Is the amount of any of these changing at this time?

What is the origin & structure of our solar system?

1.1 Our Galaxy & Solar System

Distinguish among galaxies, stars, and planets. Differentiate between the key distances of our solar system and locate Earth.

• Our solar system—the Sun and eight planets—is located on a trailing edge of the Milky Way Galaxy. Gravity, the mutual attract- ing force exerted by all objects upon all other objects in proportion to their mass, is an organizing force in the universe. Solar systems form when stars (like our Sun) condense from nebular dust and gas, with planets forming in orbits around these central masses.

1. Describe the Sun’s status among stars in the Milky Way Galaxy. Describe the Sun’s location, size, and relationship to its planets.

2. Diagram in a simple sketch Earth’s orbit about the Sun. How much does it vary during the course of a year?

1.2 Solar Energy from Sun to Earth

Describe the Sun’s operation, including solar wind.

• The fusion process within the Sun generates incredible quanti- ties of energy. Solar wind is deflected by Earth’s magnetosphere, producing various effects in the upper atmosphere, including the northern and southern lights. Solar wind may also influ- ence weather.

3. How does the Sun produce such tremendous quantities of energy?

1.3 Electromagnetic Spectrum of Radiant Energy

Explain the characteristics of the electromagnetic spectrum of radiant energy.

• Radiant energy travels outward from the Sun in all directions, rep- resenting a portion of the total electromagnetic spectrum made up of different energy wavelengths. A wavelength is the distance between corresponding points on any two successive waves.

4. What are the main wavelengths produced by the Sun? Which wavelengths does Earth radiate to space?

1.4 Incoming Energy & Net Radiation

Describe the global pattern of net radiation.

• Incoming electromagnetic radiation from the Sun is insolation. The subsolar point is where solar rays are perpendicular to the Earth’s surface (radiating from directly overhead). All other lo- cations away from the subsolar point receive slanting rays and more diffuse energy.

• The angle of incoming sunlight is different at each latitude because Earth’s surface is curved. This causes an uneven distribution of insolation and heating. Higher latitude regions receive less insola- tion than the tropics mainly because of the lower angle of the Sun.

5. Study Figure 1.9. How does net radiation in the tropics compare with net radiation at the poles?

Chapter 1 Review

M01_CHRI4744_01_SE_C01.indd 27 23/01/16 1:59 PM

Visual Analysis

28 Chapter 1 Review

1.9 Variable Atmospheric Components

Distinguish between natural and anthropogenic pollutants in the lower atmosphere.

• The spatial aspects of natural and human-caused pollutants are important topics in physical geography and have serious human health implications

• Wildfires and volcanoes are natural sources of air pollution. Wildfires burn larger areas, in part due to climate change.

• Winds, local and regional landscapes, and temperature inver- sions all can concentrate pollution.

12. Why does a temperature inversion worsen an air pollution episode?

1.10 Anthropogenic Pollution

Construct a simple diagram illustrating the pollution from photochemical reactions in motor vehicle exhaust. Describe the sources and effects of industrial smog, acid deposition, and particulates. Discuss the Clean Air Act’s impact on air pollution.

• Anthropogenic air pollution is responsible for roughly 2% of annual deaths in the United States, China, India, as well as Canada, Europe, and Mexico.

• Photochemical smog results from the interaction of sunlight and the products of automobile exhaust.

• Human-produced industrial smog over North America, Europe, and Asia is related to coal-burning power plants.

13. Summarize the cost–benefit results from the first 20 years under Clean Air Act regulations.

1.7 Atmospheric Temperature

Draw a diagram showing a profile of atmospheric structure based on temperature.

• Using temperature as a criterion, we identify the thermosphere as the outermost layer, corresponding roughly to the heterosphere in location. Its upper limit is at an altitude of approximately 480 km.

• In the homosphere, temperature criteria define the mesosphere, stratosphere, and troposphere.

9. Draw and label a diagram showing the structure of the atmos- phere based on its temperature.

1.8 Atmospheric Function

Draw a diagram showing a profile of atmospheric structure based on function.

Describe conditions within the stratosphere. Summarize the function and status of the ozonosphere, or ozone layer.

• The outermost region by function is the ionosphere, extending through the heterosphere and partway into the homosphere. It absorbs cosmic rays, gamma rays, X-rays, and shorter wavelengths of ultraviolet radiation and converts them into kinetic energy. Within the stratosphere, the ozonosphere, or ozone layer, absorbs ultraviolet radiation, raising the temperature of the stratosphere.

• The reduction of stratospheric ozone, the ozone layer, by CFCs during the past several decades is a hazard for society and many natural systems.

10. What are the two primary functional layers of the atmosphere and what does each do?

11. Why is stratospheric ozone so important? Describe the effects created by increases in ultraviolet light reaching the surface.

1. Describe what is happening in this photograph of Salt Lake City, Utah, in winter. What is this phenomenon called?

2. If you could measure changes in air temperature from near the ground up to about the same altitude as the mountaintops, how would the air temperature change? Explain.

Critical Thinking

1. If the Sun were hotter, how would that change the curve of energy distribution by wavelength (Fig. 1.6)?

2. Given that Earth is closest to the Sun in January and farthest from the Sun in July, why is July warmer than January in the Northern Hemisphere?

3. How does Earth’s axial tilt relate to seasonality? How would a greater axial tilt affect seasonality?

4. How could you evaluate the relative harm of anthropogenic air pollution versus natural air pollution?

5. How is the percentage of people suffering from asthma related to the percentage living in urban areas? What is one likely explanation of this correlation?

▶ R1.1

M01_CHRI4744_01_SE_C01.indd 28 23/01/16 1:59 PM

Chapter 1 Review 29

• Open: MapMaster in MasteringGeography • Select: Insolation, then select Vegetation from the Physical Environ-

ment menu.

The Insolation layer shows annual mean insolation in watts per square meter received at the surface, and the Vegetation layer shows world plant regions.

1. What are the insolation values associated with desert shrub vegetation?

2. What are the insolation values associated with tropical forest vegetation?

3. What is the insolation value for where you live? What type of vegetation is found there?

Interactive Mapping

Insolation

Seasonal Declination Changes

Google Earth allows you to model sunlight for any day and time. We can use this to see how the position of the circle of illumina- tion moves during the year. Open Google Earth, zoom out so you can see the entire Earth. Click the Sun button, found between the Sky view button and the Historic imagery button. Move the earth until you can see the dividing line between day and night. Click on the wrench button in the Date and Time Options pop-up window. Click on the month in the End date/time box. Click through the entire year by using the up arrow in the End date/ time box. Although the circle of illumination is just an artistic depiction of the actual circle of illumination, we can still use it for some general analysis.

1. Which areas would have 24 hours of darkness on 12/21? (You may have to tilt the Earth so you can see each of the poles.)

2. Which areas would have 24 hours of light on 12/21?

Explore

Looking for additional review and test prep materials? Visit the Study Area in MasteringGeography™ to enhance your geographic literacy, spatial reasoning skills, and understanding of this chapter’s content by accessing a variety of resources, including MapMaster™

interactive maps, videos, Mobile Field Trips, Project Condor Quadcopter videos, In the News RSS feeds, flashcards, web links, self-study quizzes, and an eText version of Geosystems Core.

air (p. 16) air pressure (p. 16) altitude (p. 12) Antarctic Circle (p. 14) Arctic Circle (p. 14) auroras (p. 7) autumnal equinox

(p. 27) axial parallelism (p. 13) axial tilt (p. 13) axis (p. 13) circle of illumination

(p. 13) day length (p. 12)

December solstice (p. 14) declination (p. 12) electromagnetic

spectrum (p. 8) environmental lapse rate

(p. 19) exosphere (p. 16) fusion (p. 6) gravity (p. 4) heterosphere (p. 17) homosphere (p. 17) industrial smog (p. 24) insolation (p. 10) ionosphere (p. 20)

June solstice (p. 14) kinetic energy (p. 18) magnetosphere (p. 7) March equinox (p. 14) mesosphere (p. 18) Milky Way Galaxy (p. 4) nitrogen dioxide (NO2)

(p. 24) normal lapse rate

(p. 19) oxygen (p. 17) ozone layer (p. 20) particulate matter (PM)

(p. 25)

photochemical smog (p. 24)

plane of the ecliptic (p. 13)

pollutants (p. 22) revolution (p. 13) rotation (p. 13) sensible heat (p. 18) September equinox (p. 14) solar constant (p. 10) solar wind (p. 6) speed of light (p. 5) stratosphere (p. 19) subsolar point (p. 10)

sulfur dioxide (SO2) (p. 24)

summer solstice (p. 14) sunspots (p. 6) temperature inversion

(p. 23) thermosphere (p. 18) Tropic of Cancer (p. 12) Tropic of Capricorn (p. 14) tropopause (p. 19) troposphere (p. 19) wavelength (p. 8) winter solstice (p. 14) vernal equinox (p. 27)

Key Terms

3. The Sun is perpen- dicular to the circle of illumination. Click through the weeks until it ap- pears that the cir- cle of illumination passes through both poles and the Sun’s declination is 0°. What day does this occur on in Google Earth? What seasonal event is this? When is the Sun directly over the equator?

4. Continue to click through the year until the circle of illumina- tion is illuminating the largest area north of the Arctic Circle. You might want to tilt Earth so you can see all of the Arctic Circle. On what day does it appear that there is the most illumination north of the Arctic Circle? What seasonal event is this?

Use Google Earth to explore seasonal changes in the Sun’s declination.

▲ R1.2

M01_CHRI4744_01_SE_C01.indd 29 30/01/16 5:44 PM

GeoLab1

Seasonal Changes: What is the role of latitude in changing insolation & day length? Over the course of a year, the area where we live experiences seasonal changes in the amount of insolation it receives, the angle of the Sun, and the length of daylight. Seasonal changes in insolation for a particular location are largely driven by the angle of the Sun above the ground, and the length of daylight--both of which depend on the latitude of that location.

Apply In this lab, you will be working as an analyst for an electrical power company that is planning to build a number of new solar power genera- tion arrays at different locations. To help assess the energy potential of each location, you will use charts and graphs to determine insolation amounts and the Sun’s altitude, estimate day length during the year, and track the path of the Sun. This information has applications in areas ranging from agriculture to architecture and urban design.

Objectives • Analyze seasonal changes in insolation • Estimate day length • Calculate hourly insolation values

Procedure I: Tracking Daily Insolation Figure GL 1.1 shows daily insolation as a func- tion of time of year and latitude. Refer to the chart to answer the questions below.

1. How much insolation is received at 0° N on the summer solstice? On the winter solstice? How much does insolation vary from summer to winter at this location?

2. How much insolation is received at 40° N on the summer solstice? On the winter solstice? How much does insolation vary from summer to winter at this location?

3. How much insolation is received at 60° N on the summer solstice? On the winter

solstice? How much does insolation vary from summer to winter at this location?

4. How much insolation is received at 90° N on the summer solstice? On the winter solstice? How much does insolation vary from summer to winter at this location?

5. What is your latitude? How much insolation is received at that location on the summer solstice? On the winter solstice? How much does insolation vary from summer to winter at your location?

6. How does the difference between summer and winter insolation vary with latitude? Which latitudes have the most consistent insolation?

▲ GL1.1 Spain’s Gemasolar array

the online portion of this lab, view the Pre-Lab

Video, and complete the Post-Lab Quiz.

www.masteringgeography.com

GeoLab1 Pre-Lab Video

https://goo.gl/pHJn0k

M01_CHRI4744_01_SE_C01.indd 30 25/01/16 12:07 PM

1 Solar Energy, Seasons, & the Atmosphere 31

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Latitude

Daily Receipt of Insolation (W/m2) at Top of the Atmosphere

Subsolar Point

North Pole

Arctic Circle

New York, Rome

Tropic of Cancer

Equator

Tropic of Capricorn

New Zealand

Antarctic Circle

South Pole

100

150

200

250

300

350

400

50 100 150 200 250 300 350

400

45 0

50 0

550

55 0

500

450

400

350

300

250

200 150 100

450

50 0

V er

n al

e q

u in

o x

A ut

um na

l e qu

in ox

Su m

m er

s o

ls ti

W in

te r

so ls

ti ce

▲ GL1.2 Daily insolation received at the top of the atmosphere. The total daily insolation received at the top of the atmosphere is charted in watts per square meter per day by latitude and month. (1 W/m2/day = 2.064 cal/cm2/day).

Table GL 1.1 Day length––the time between sunrise and sunset––at selected latitudes for the Northern Hemisphere. Winter Solstice

(December Solstice) December 21–22

Vernal Equinox (March Equinox)

March 20–21

Summer Solstice (June Solstice)

June 20–21

Autumnal Equinox (September Equinox)

September 22–23

A.M. P.M. Day length A.M. P.M. Day length A.M. P.M. Day length A.M. P.M. Day length

0º 6:00 6:00 12 __________ 6:00 6:00 12 __________ 6:00 6:00 12 __________ 6:00 6:00 12 __________

30º 6:58 5:02 __________ 6:00 6:00 12 __________ 5:02 6:58 __________ 6:00 6:00 12 __________

40º 7:26 4:34 __________ 6:00 6:00 12 __________ 4:34 7:26 __________ 6:00 6:00 12 __________

50º 8:05 3:55 __________ 6:00 6:00 12 __________ 3:55 8:05 __________ 6:00 6:00 12 __________

60º 9:15 2:45 __________ 6:00 6:00 12 __________ 2:45 9:15 __________ 6:00 6:00 12 __________

90º No sunlight Rising Sun Continuous sunlight Setting Sun

Procedure II: Tracking Seasonal Variations Table GL.1.1 shows the hours of daylight at different latitudes in the Northern Hemisphere.

7. Calculate day length for 30° N, 40° N, 50° N, 60° N, and your latitude. Enter the values in Table GL1.1.

8. What is the average hourly insolation at the Equator on the summer solstice? To find this value, divide the daily inso- lation value by the number of hours in the day.

9. What is the average hourly insolation at 40° N on the summer solstice? On the winter solstice?

10. What is the average hourly insolation at 90° N on the summer solstice?

11. What is the average hourly insolation at your latitude on the summer solstice? On the winter solstice?

12. Which of these locations receives the most intense (highest watts per hour per square meter) insolation? How many watts per hour per square meter does this location receive, and when does this occur?

Analyze & Conclude

13. Figure GL.1.1 shows changes in insola- tion related to the angle of the Sun and day length. However, the amount of insolation over the poles varies. How does the maximum insolation at the North Pole’s summer solstice compare to the maximum insolation at the South Pole’s summer solstice? What other Earth–Sun relationship could explain this difference?

14. Do you think that latitude or day length is more important in insolation? Compare the North Pole with 40° N and with the equator in your analysis and explain your answer.

15. Your company plans to build three solar power arrays, at 30° N, 40° N, and 50° N. What is one main way in which the design

of each array would need to differ, assum- ing each is intended to generate the same amount of power? Explain your answer.

16. Your company is considering building solar power arrays near the Arctic Circle in Alaska and Canada. What are the advan- tages and disadvantages of these loca- tions for solar power?

Geosystems Core: GeoLab1 31

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