Chapter 1, Review Questions



Chapter 3, Review Questions

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1. What is the basis for subdividing the electromagnetic spectrum into various forms of electromagnetic radiation?

a. The electromagnetic spectrum is subdivided because we detect, measure, generate and use the forms differently. They have varying wavelengths, frequencies and are used for different purposes, including medical and communication.

2. What is a blackbody? Is the Earth-atmosphere system a blackbody?

a. A blackbody is a perfect radiator, that is, it absorbs all incident radiation at all wavelengths and emits all radiation at all wavelengths. No radiation is reflected or transmitted. Blackbody does not refer to the color of the radiating object. The Earth-atmosphere system is not a blackbody.

3. Apply Wien’s displacement law in comparing the radiational properties of the Sun versus those of the Earth-atmosphere system.

a. Wien’s displacement law states that with increasing absolute temperature, the wavelength of the maximum radiation emitted or absorbed will decrease. Therefore hot objects such as the sun emit radiation that peaks at shorter wavelengths than relatively cool objects such as Earth.

4. How does the solar altitude affect the length of the path of solar radiation through Earth’s atmosphere?

a. With increasing solar altitude, the sun’s rays striking the Earth’s surface become more concentrated, that is, more energy is received per unit area. Also, with increasing solar altitude, the solar beam’s path length through the atmosphere decreases, reducing the attenuation of incoming solar radiation by reflection, scattering, and absorption.

5. In the Northern Hemisphere, Earth is closer to the Sun during the winter than during the summer and yet winter is colder than summer. An explanation please.

a. Winters are colder than summers because maximum solar altitudes are lower (less intense solar radiation striking Earth’s surface) and daylight is shorter in winter than in summer.

6. What is the significance of the Tropic of Cancer and the Tropic of Capricorn?

a. At 23.5 degrees N and S latitudes respectively, the Tropics of Cancer and Capricorn mark the poleward boundaries of the zone of the Earth where at certain times during the year the noon sun reaches an altitude of 90 degrees (directly overhead).

7. Describe the interactions of incoming solar radiation with the components of the atmosphere.

a. These interactions consist of scattering, reflection, and absorption. In the process of scattering, a particle disperses solar radiation in all directions—up, down, and sideways. Reflection is a special case of scattering where some of the solar radiation striking an interface between two different media is backscattered. During absorption some of the radiation striking the surface of an object is converted to heat energy.

8. Why does the Antarctic ozone hole appear in the Southern Hemisphere spring?

a. During the winter months in the Southern Hemisphere, polar stratospheric clouds form. These clouds contain water particles that allow chlorine and bromine compounds to form and cause ozone depletion. During the spring and summer months, the sun’s radiation supplies the energy needed to repair the ozone hole.

9. All other factors being the same, how does a snow cover affect the day’s maximum and minimum air temperatures?

a. The surface of a fresh cover of snow reflects back to the atmosphere 80% or more of the incident solar radiation. Very little solar radiation is converted to heat energy. Radiant energy, which might have been absorbed and then transferred as heat energy to the air above to warm it, instead is reflected back to space without doing any heating. Much of the small amount of radiation that is absorbed converts ice to liquid water or water vapor. Snow is very nearly a blackbody in the infrared so that at night a snow cover radiates very efficiently to space (especially during clear skies). Hence, a snow cover lowers both the daily maximum and minimum air temperature.

10. Provide a convincing argument that water vapor is the principal greenhouse gas.

a. Water vapor is the principle greenhouse gas because it causes the greatest amount of warming at Earth’s surface. For example, in areas with very little water vapor in the air, infrared radiation is able to escape into space at night. In areas with a great amount of cloud cover or high tropospheric water vapor content, water vapor strongly absorbs infrared radiation emitted by Earth and emits some IR back to Earth’s surface, warming the surface.

Chapter 3, Critical Thinking Questions

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1. How is global radiative equilibrium an example of the law of energy conservation?

a. The law of energy conservation means that on a global scale, the input of solar radiation must equal the output of terrestrial infrared radiation to space. An imbalance would cause temperatures on Earth to rise or fall (depending on the direction of the imbalance) until a new equilibrium is established. Due to a relatively constant planetary temperature, we can assume that Earth is receiving the same amount of energy that is being emitted back to space.

2. Compare Earth’s planetary albedo to the albedo of the Moon. Why the difference?

a. No clouds in the lunar atmosphere means that the moon’s albedo is lower than that of Earth but no ocean on the moon favors a higher albedo on the moon. Absence of clouds is the more important of the two factors so that the albedo of the moon is considerably less than Earth’s planetary albedo.

3. Speculate on what Earth’s climate would be like if the planet had no greenhouse effect.

a. With no greenhouse effect the mean temperature at the Earth’s surface would be some 33 Celsius degrees (59 Fahrenheit degrees) lower than it is today—much too cold for most life forms to exist.

4. Why does atmospheric carbon dioxide concentration exhibit an annual cycle?

a. Levels of carbon dioxide decrease during the growing season due to increased vegetation and increase during the winter months reaching a maximum in May.

5. Although the Keeling curve and the trend in global mean annual temperature show increasing trends, the two curves are not parallel. Explain why.

a. The Keeling curve is a depiction of carbon dioxide levels at one location in Hawaii. The global annual mean temperature includes land and ocean as well as higher latitudes which may be experiencing polar amplification of global climate change.

6. The concentration of Methane in the atmosphere is measured in parts per billion by volume (ppbv). Why then is methane considered an important greenhouse gas?

a. Methane is also an infrared absorbing gas that is increasing in the atmosphere. Although it has fluctuated over the past 400,000 years, it is now at its greatest concentration. It is on the rise do to rice cultivation, cattle, landfills, termites, coal mining, wastewater treatment and petroleum systems.

7. Suggest some strategies that promise to reduce the amount of carbon dioxide vented to the atmosphere.

a. Carbon dioxide vented into the atmosphere can be reduced by changing certain human factors such as: reductions in coal and oil consumption, using less fossil fuel energy sources, better energy efficiencies, the end to deforestation, and massive reforestation.

8. What is the significance of the Stefan-Boltzmann law when applied to the Sun versus the Earth-atmosphere system?

a. The Stefan-Boltzmann law shows that small changes in the temperature of a blackbody result in a much greater change in radiational energy. The Sun’s temperature is much greater than that of Earth, therefore its energy output is 190,000 times that of Earth’s.

9. According to the inverse square law, if the distance between Earth and the Sun were triple its present magnitude; the solar constant would be reduced to what fraction of its present value?

a. If the distance between Earth and Sun tripled, the solar constant would be reduced to 1/9 its present value.

10. On the equinox, the length of daylight is not precisely 12 hours. Explain why?

a. The sunrise and sunset times vary due to optical effects of the atmosphere on the solar beam. The incoming solar beam refracts downward so that the sun appears to be higher than it actually is. This lengthens the period of daylight.

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