The Energy-Atmosphere System

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PART ONE:

The Energy-Atmosphere System

Geosystems begins with the Sun and Solar System to launch the first of four parts. Our planet and our lives are powered by radiant energy from the star closest to Earth—the Sun. Each of us depends on many systems that are set into motion by energy from the Sun. These systems are the subjects of Part One.

Part One exemplifies the systems organization of the text: it begins with the origin of the solar system and the Sun. Solar energy passes across space to Earth’s atmosphere varying seasonally in its effects on the atmosphere (Chapter 2). Insolation then passes through the atmosphere to Earth’s surface (Chapter 3). From Earth’s surface, and surface energy balances (Chapter 4) generate patterns of world temperature (Chapter 5) and general and local atmospheric circulation (Chapter 6). Each of the text’s four parts contains related chapters with content arranged according to the flow of individual systems or in a manner consistent with time and the flow of events.

The Part-opening photo shows The Midnight Sun seen from a research ship in the Arctic Ocean. The camera points due north, viewing the Sun’s rays from across the North Pole some 885 km (550 mi) distant (see the inset illustration). The author commented that it seemed strange at the time to have natural lighting that felt like about 3 P.M. (15:00 hours), yet his watch clearly showed it to be midnight. See Figure 2.16 for a near-midnight Antarctic scene.

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Solar Energy to Earth

and the Seasons

2

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Overview

The ultimate spatial inquiry is to know the location of Earth in the Universe. To properly set the stage for a course in the physical geography of Earth, slides, videography, Internet sites, and posters can be used to establish the location and place of our planetary home. Our immediate home is North America, a major continent on planet Earth, the third planet from a typical yellow star in a solar system. That star, our Sun, is only one of billions in the Milky Way Galaxy, which is one of billions of galaxies in the Universe.

This chapter examines the nature of the flow of energy and material from the Sun to the outer reaches of Earth’s atmosphere. The top of the atmosphere is a measuring point to assess the arriving solar energy. Earth receives solar wind and electromagnetic radiation from the Sun.

Earth’s orientation to the Sun varies seasonally. The chapter ends with a discussion of seasons and seasonal changes in insolation and daylength.

As before, a list of key learning concepts begins the chapter and is used to organize the Summary and Review section, with definitions, key terms and page numbers, and review questions grouped under each objective. At the beginning of each chapter a section titled “In This Chapter” introduces the chapter’s content in a succinct statement.

Outline Headings and Key Terms

The first-, second-, and third-order headings that divide Chapter 2 serve as an outline. The key terms and concepts that appear boldface in the text are listed here under their appropriate heading in bold italics. All these highlighted terms appear in the text glossary. Note the check-off box ()so you can mark class progress. The students have this same list in their Student Study Guide. The icon indicates that there is accompanyingmaterialon the Student CD.

The outline headings and terms for Chapter 2:

Milky Way Galaxy

The Solar System, Sun, and Earth

 Nebular Hypothesis

Solar System Formation and

Structure

gravity

planetesimal hypothesis

Dimensions and Distances

speed of light

Earth’s Orbit

perihelion

aphelion

plane of the ecliptic

Solar Energy: From Sun to Earth

Electromagnetic Spectrum and Plants

fusion

Solar Activity and Solar Wind

solar wind

sunspots

Solar Wind Effects

magnetosphere

auroras

Weather Effects

Electromagnetic Spectrum of

RadiantEnergy

electromagnetic

spectrum

wavelength

Incoming Energy at the Top

of the Atmosphere

thermopause

insolation

Solar Constant

solar constant

Uneven Distribution of Insolation

subsolar point

Global Net Radiation

The Seasons

 Earth-Sun Relations, Seasons

Seasonality

altitude

declination

daylength

Reasons for Seasons

Revolution

revolution

Rotation

rotation

axis

circle of illumination

Tilt of Earth’s Axis

axial tilt

Axial Parallelism

axial parallelism

Sphericity

Annual March of the Seasons

sunrise

sunset

winter solstice

December solstice

vernal equinox

March equinox

summer solstice

June solstice

autumnal equinox

September equinox

Dawn and Twilight

Seasonal Observations

SUMMARY AND REVIEW

News Reports

News Report 2.1: The Nature of Order Is Chaos

News Report 2.2: Monitoring Earth Radiation Budget

URLs listed in Chapter 2

Solar systems simulator:

Sunspot cycle and auroral activity:

International Earth Rotation Service:

Sunrise, sunset calculator:

sunrise.html

URLs of Interest

Hubble telescope and astronomy info:

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Key Learning Concepts for Chapter 2

The following learning concepts help guide the student’s reading and comprehension efforts. The operative word is in italics. These are included in each chapter of Geosystems and the Geosystems Student Study Guide. The student is told: “after reading the chapter you should be able to”:

• Distinguish among galaxies, stars, and planets, and locate Earth.

• Overview the origin, formation, and development of Earth and the atmosphere and construct Earth’s annual orbit about the Sun.

• Describe the Sun’s operation, and explain the characteristics of the solar wind and the electromagnetic spectrum of radiant energy.

• Portray the intercepted solar energy and its uneven distribution at the top of the atmosphere.

•Define solar altitude, solar declination, and daylength; describe the annual variability of each—Earth’s seasonality.

Annotated Chapter Review Questions

• Distinguish among galaxies, stars, and planets, and locate Earth.

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

Our Sun is both unique to us and commonplace in our galaxy. It is only average in temperature, size, and color when compared with other stars, yet it is the ultimate energy source for almost all life processes in our biosphere. Planets do not produce their own energy. Our Sun is located on a remote, trailing edge of the Milky Way Galaxy, a flattened, disk-shaped mass estimated to contain up to 400 billion stars.

2. If you have seen the Milky Way at night, briefly describe it. Use specifics from the text in your description.

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. On a clear night the naked eye can see only a few thousand of the nearly 400 billion stars.

3. Briefly describe Earth’s origin as part of the Solar System.

According to prevailing theory, our Solar System condensed from a large, slowly rotating, collapsing cloud of dust and gas called a nebula. As the nebular cloud organized and flattened into a disk shape, the early proto-Sun grew in mass at the center, drawing more matter to it. Small accretion (growing) eddies—the protoplanets—swirled at varying distances from the center of the solar nebula. The early protoplanets, or planetesimals, were located at approximately the same distances from the Sun that the planets are today. The beginnings of the Sun and the solar system are estimated to have occurred more than 4.6 billion years ago. These processes are now observed as occurring elsewhere in the galaxy. Astronomers so far have observed almost two dozen stars with planets orbiting about them.

4. Compare the locations of the nine planets of the Solar System.

See Figure 2.1c and d for this information. There is a Solar System simulation at .

• Overview the origin, formation, and development of Earth and the atmosphere and construct Earth’s annual orbit about the Sun.

5. How far is Earth from the Sun in terms of light speed? In terms of kilometers and miles?

Earth’s orbit around the Sun is presently elliptical—a closed, oval-shaped path (Figure 2.1d). Earth’s average distance from the Sun is approximately 150 million km (93 million mi). Divided by the speed of light, this places us 8 minutes and 20 seconds from the Sun. In other words it takes light that time to travel across planetary space to Earth.

6. Briefly describe the relationship among these concepts: Universe, Milky Way Galaxy, Solar System, Sun, and Planet Earth.

The Universe is infinite in size and dimension from our perspective. Tens of billions of galaxies are known to populate the Universe we can observe, each composed of hundreds of billions of stars. Our Sun is a typical yellow-dwarf thermonuclear (fusion) star, somewhat less than a million miles in diameter. Planets orbit about stars such as our Solar System. Our Sun and the orbiting planets are revolving around the Milky Way Galaxy in a vast clockwise spiral.

Similar multiple-planet solar systems are now being studied through the Hubble and other telescopes. More than 60 planets outside our Solar Systems are now identified and planets forming in a manner similar to how scientists think Earth formed are being observed. The astronaut-delivered upgrade on the Hubble that took place in 2002 has produced astounding results since the already prodigious power wasincreased a full ten times and the thermal infrared telescope was restored.

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

Earthisatperihelion(itsclosestpositiontotheSun)duringtheNorthernHemispherewinter(January3at147,255,000km,or91,500,000mi).It is at aphelion(itsfarthestpositionfromtheSun)duringtheNorthernHemispheresummer(July4at152,083,000km,or94,500,000mi).ThisseasonaldifferenceindistancefromtheSuncausesaslightvariationinthesolarenergyinterceptedbyEarth,butisnotanimmediatereasonforseasonalchange.

• Describe the Sun’s operation and explain the characteristics of the solar wind and the electromagnetic spectrum of radiant energy.

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

The solar mass produces tremendous pressure and high temperatures deep in its dense interior region. Under these conditions, pairs of hydrogen nuclei, the lightest of all the natural elements, are forced to fuse together. This process of forcibly joining positively charged nuclei is called fusion. In the fusion reaction hydrogen nuclei form helium, the second lightest element in nature, and liberate enormous quantities of energy in the form of free protons, neutrons, and electrons. During each second of operation, the Sun consumes 657 million tons of hydrogen, converting it into 652.5 million tons of helium. The difference of 4.5 million tons is the quantity that is converted directly to energy—resulting in literally disappearing solar mass.

9. What is the sunspot cycle? At what stage was the cycle in 2001?

A regular cycle exists for sunspot occurrences, averaging 11 years from maximum peak to maximum peak; however, the cycle may vary from 7 to 17 years. In recent cycles, a solar minimum occurred in 1976, whereas a solar maximum took place in 1979, when over 100 sunspots were visible. Another minimum was reached in 1986, and an extremely active solar maximum occurred in 1990 with over 200 sunspots, 11 years from the previous maximum, in keeping with the average. In 1997, we witnessed a solar minimum. In2001, the cycle returned to an intense maximum, causing auroras to be visible at lower latitudes. The minimum may have been reached in 2007, with cycle 24 beginning in 2008 and forecast to reach a maximum in 2012.

10. Describe Earth’s magnetosphere and its effects on the solar wind and the electromagnetic spectrum.

Earth’s outer defense against the solar wind is the magnetosphere, which is a magnetic force field surrounding Earth, generated by dynamo-like motions within our planet. As the solar wind approaches Earth, the streams of charged particles are deflected by the magnetosphere and course along the magnetic field lines. The extreme northern and southern polar regions of the upper atmosphere are the points of entry for the solar wind stream.

11. Summarize the presently known effects of the solar wind relative to Earth’s environment.

The interaction of the solar wind and the upper layers of Earth’s atmosphere produces some remarkable phenomena relevant to physical geography: the auroras, disruption of certain radio broadcasts and even some satellite transmissions, and possible effects on weather patterns.

12. Describe the segments of the electromagnetic spectrum, from shortest to longest wavelength. What wavelengths are mainly produced by the Sun? Which are principally radiated by Earth to space?

See Figures 2.6 and 2.7. All the radiant energy produced by the Sun is in the form of electromagnetic energy and, when placed in an ordered range, forms part of the electromagnetic spectrum. The Sun emits radiant energy composed of 8% ultraviolet, X-ray, and gamma ray wavelengths; 47% visible light wavelengths; and 45% infrared wavelengths. Wavelengths emitted from the Earth back to the Sun are of lower intensity and composed mostly of infrared wavelengths.

• Portray the intercepted solar energy and its uneven distribution at the top of the atmosphere.

13. What is the solar constant? Why is it important to know?

The average value of insolation received at the thermopause (on a plane surface perpendicular to the Sun’s rays) when Earth is at its average distance from the Sun. That value of the solar constant is 1372 watts per square meter (W/m2). A watt is equal to one joule (a unit of energy) per second and is the standard unit of power in the SI-metric system. (See Appendix C in Geosystems for more information on measurement conversions.) In nonmetric calorie heat units, the solar constant is expressed as approximately 2 calories (1.968) per cm2 per minute, or 2 langleys per minute (a langley being 1 cal per cm2). A calorie is the amount of energy required to raise the temperature of one gram of water (at 15° C) one degree Celsius and is equal to 4.184 joules.

Knowing the amount of insolation intercepted by Earth is important to climatologists and other scientists as a basis for atmospheric and surface energy measurements and calculations.

14. Select 40° or 50° north latitude on Figure 2.10, and plot the amount of energy in W/m2 per day characteristic of each month throughout the year. Compare this to the North Pole; to the equator.

See Figure 2.10. Note the watts per m2 received at each month for specific latitudes. Graphs at key latitudes are placed along the right-hand side of the chart.

15. If Earth were flat and oriented perpendicular to incoming solar radiation (insolation), what would be the latitudinal distribution of solar energy at the top of the atmosphere?

The atmosphere is like a giant heat engine driven by differences in insolation from place to place (see Figure 2.9). If Earth were flat there would be an even distribution of energy by latitude with no differences from place to place and therefore little motion produced.

• Define solar altitude, solar declination, and daylength and describe the annual variability of each—Earth’s seasonality.

16. Assess the 12-month Gregorian calendar, with its months of different lengths, and leap years, and its relation to the annual seasonal rhythms—the march of the seasons. What do you find?

The Gregorian calendar in common use has no relation to natural rhythms of Sun, Earth, the Moon, and the march of the seasons.

17. The concept of seasonality refers to what specific phenomena? How do these two aspects of seasonality change during the year at 0° latitude? At 40°? At 90°?

Seasonality refers to both the seasonal variation of the Sun’s rays above the horizon and changing daylengths during the year. Seasonal variations are a response to the change in the Sun’s altitude, or the angular difference between the horizon and the Sun. Seasonality also means a changing duration of exposure, or daylength, which varies during the year depending on latitude. People living at the equator always receive equal hours of day and night, whereas people living along 40° N or S latitude experience about six hours’ of difference in daylight hours between winter and summer; those at 50° N or S latitude experience almost eight hours of annual daylength variation. At the polar extremes the range extends from a six-month period of no insolation to a six-month period of continuous 24-hour days.

18. Differentiate between the Sun’s altitude and its declination at Earth’s surface.

The Sun’s altitude is the angular difference between the horizon and the Sun. The Sun is directly overhead at zenith only at the subsolar point. The Sun’s declination—that is, the angular distance from the equator to the place where direct overhead insolation is received—annually migrates through 47 degrees of latitude between the two tropics at 23.5° N and 23.5° S latitudes.