1. Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Chapter 2 The Earth’s Global Energy Balance

2. Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Chapter Overview Electromagnetic Radiation Insolation over the Globe Composition of the Atmosphere Sensible Heat and Latent Heat Transfer The Global Energy System Net Radiation, Latitude, and the Energy Balance

3. Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Electromagnetic Radiation Electromagnetic Radiation: wavelike form of energy radiated by any substance possessing heat; travels through space at speed of light

4. Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Electromagnetic Radiation Radiation and Temperature Principles: 1. Hot objects radiate more energy than cooler objects 2. The hotter the object, the shorter the wavelengths of energy it emits

5. Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Electromagnetic Radiation Solar Radiation Solar energy is generated by nuclear fusion Solar energy travels at speed of light (300,000 km/second) Takes 8 1/3 minutes to travel from Sun to Earth Solar constant: 1367 W/m 2

6. Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Electromagnetic Radiation Characteristics of Solar Energy Solar output peaks in the visible part of the spectrum Some wavelengths of solar radiation are absorbed and scattered in the atmosphere Absorption: process in which electromagnetic energy is transferred to heat energy when radiation strikes molecules or particles in a gas, liquid, or solid Scattering: process in which particles and molecules deflect incoming solar radiation in different directions on collision

7. Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Electromagnetic Radiation Characteristics of Solar Energy Absorption and scattering in the atmosphere: Absorption warms the atmosphere directly Solar rays can be scattered back to space or down toward Earth Shortwave radiation: electromagnetic energy in the range from 0.2 to 3 µm

8. Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Electromagnetic Radiation Longwave Radiation from the Earth Earth radiates less energy than the sun Energy from Earth is radiated at longer wavelengths Some wavelengths emitted by Earth are absorbed in the atmosphere Longwave radiation: electromagnetic radiation in the range from 3 to 50 µm

9. Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Insolation over the Globe Insolation is incoming solar radiation Measured in W/m 2 Depends on angle of the sun above the horizon

10. Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Insolation over the Globe Daily Insolation Through the Year Average insolation over a 24-hour day depends on: 1. Angle at which Sun’s rays strike Earth  Controlled by latitude, time of year, time of day 2. How long the place is exposed to Sun’s rays  Controlled by latitude and time of year Insolation: the flow of solar energy intercepted by an exposed surface assuming a uniformly spherical Earth with no atmosphere

11. Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Insolation over the Globe Annual Insolation by Latitude Annual insolation decreases from equator to poles, But, tilt of Earth’s axis redistributes significant insolation from equator towards the poles

12. Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Insolation over the Globe Equatorial: intense insolation, day and night roughly equal Tropical: high annual insolation, marked seasonal cycle Subtropical: large annual insolation; strong seasonal cycle Midlatitude: strong seasonal contrasts in insolation and length of day Arctic/subarctic, Antarctic/subantarctic: enormous variation in annual insolation, extreme variation in daylength Polar: greatest seasonal insolation contrasts, 6-month day, 6-month night World Latitude Zones Equator to poles: decreasing insolation, stronger seasonality

13. Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Composition of the Atmosphere Air is a mixture of gases Dry Air: 78% nitrogen, 21% oxygen, with argon, carbon dioxide, other gases Atmosphere also contains water vapor, tiny particles Carbon dioxide (CO 2 ): needed by green plants, absorbs long-wave radiation Water vapor varies up to 2%, absorbs heat

14. Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Composition of the Atmosphere Ozone in the Upper Atmosphere Ozone: form of oxygen with a molecule consisting of 3 atoms of oxygen (O 3 ) Most ozone found in stratosphere O 3, O 2, and O constantly form, are destroyed, and re-form, absorbing ultraviolet light each time Ultraviolet radiation is damaging to life, so, absorption of UV radiation by ozone layer protects life on Earth’s surface http://observe.arc.nasa.gov/nasa/ exhibits/ozone/Ozone6.html

15. Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Composition of the Atmosphere Ozone in the Upper Atmosphere Chlorofluorocarbons (CFC’s) can destroy ozone Chlorine oxide from CFC’s attacks ozone, converts it back to oxygen Less ozone=less absorption of UV radiation Surface level UV has increased about 4%/decade since 1978 Damage to skin, crops, some aquatic life 1987 treaty aimed to cut global CFC production Ozone layer expected to be restored in mid- 21 st century Ozone hole forms every year in southern hemisphere

16. Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Sensible Heat and Latent Heat Transfer Sensible heat: an indication of the intensity of kinetic energy of molecular motion within a substance Latent heat: heat absorbed and stored in a gas or liquid during the process of evaporation, melting, or sublimation Sensible heat is heat we feel; measured with a thermometer Latent heat (“hidden” heat) is energy stored and released when a substance changes state Latent heat stored when substance changes:  from solid to liquid, liquid to gas, or solid to gas Latent heat released when substance changes:  from vapor to liquid, vapor to solid, or liquid to solid

17. Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. The Global Energy System Solar Energy Losses in the Atmosphere Incoming solar radiation (shortwave): Gamma rays, x rays absorbed in outer atmosphere Most UV absorbed in ozone layer Some radiation reflected out to space Some radiation scattered (diffuse radiation) Clear sky: about 80% of radiation reaches ground Cloudy sky: increased reflection to space, and increased absorption

18. Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. The Global Energy System Albedo: proportion of solar radiation reflected upward from a surface; Earth’s average albedo varies from 0.29-0.34 High albedo: Snow and ice, also clouds Low albedo: black asphalt paving Intermediate albedo: forests, fields, bare ground Albedo of water depends on the angle of incoming radiation

19. Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. The Global Energy System Counterradiation and the Greenhouse Effect Counterradiation: longwave radiation emitted by the atmosphere Greenhouse Effect: accumulation of heat in the lower atmosphere through the absorption of longwave radiation from the Earth’s surface

20. Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. The Global Energy System Counterradiation and the Greenhouse Effect Longwave radiation from Earth absorbed by atmospheric gases: CO 2, H 2 O, other gases Increased amounts of these gases increases the absorption of heat in lower atmosphere Cloud layers (liquid water) also absorb longwave radiation

21. Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. The Greenhouse Effect and Global Energy Flows

22. Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. The Greenhouse Effect and Global Energy Flows Solar energy heats Earth Fossil fuel burning, other activities, release CO 2, other greenhouse gases Oceans transport heat, exchange heat with atmosphere Plants take up and release CO 2 Low, thick clouds cool Earth; high thin clouds warm Earth Solar energy heats Earth Oceans transport heat, exchange heat with atmosphere Plants take up and release CO 2 Low, thick clouds cool Earth; high thin clouds warm Earth Fossil fuel burning, other activities, release CO 2, other greenhouse gases

23. Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Net Radiation, Latitude, and the Energy Balance Net radiation varies with latitude Positive net radiation: energy surplus Negative net radiation: energy deficit Atmospheric circulation distributes radiation over the globe Net Radiation: the difference in energy flow between all radiant energy coming into a surface and all radiant energy leaving the surface