Understanding Heat Transfer and Solar Energy

1. Warm Up 3/6/09 • More solar energy reaches the equatorial regions than the polar regions because the equatorial regions a. are covered by a greater area of land. b. have more vegetation to absorb sunlight. c. receive sun rays closest to vertical. d. have days with more hours of sunlight. • Most important weather phenomena occur in the ____. a. stratosphere c. mesosphere b. thermosphere d. troposphere • The form of oxygen that combines three oxygen atoms into each molecule is called ____. a. ozone c. thermopause b. argon d. chlorofluorocarbon Answers: 1) c. 2) d. 3) a.

2. Heating the Atmosphere Chapter 17, Section 2

3. Energy Transfer as Heat • Heat – the energy transferred from one object to another because of a difference in their temperatures • Temperature – measure of the kinetic energy (energy of motion) of the individual atoms or molecules in a substance • Three mechanisms of energy transfer as heat are conduction, convection, and radiation

4. Heat Transfer

5. Conduction • Conduction – the transfer of heat through matter by molecular activity • The energy of molecules is transferred by collisions from one molecule to another • Heat flows from the higher temperature matter to the lower temperature matter • Different materials conduct heat better than others • Metals are good conductors, while air is a poor conductor of heat • Conduction is only important between Earth’s surface and the air directly in contact with the surface

6. Conduction

7. Convection • Much of the heat transfer that occurs in the atmosphere is carried on by convection • Convection – the transfer of heat by mass movement or circulation within a substance • Convection takes place in fluids, like the ocean and air, where the atoms and molecules are free to move about • Convection also takes place in solids, such as Earth’s mantle, which behave as fluids over long periods of time • Most of the heat acquired by radiation and conduction in the lowest layer of the atmosphere is transferred by convective flow

8. Convection

9. Concept Check • What is convection? • Convection is the transfer of heat by mass movement or circulation within a substance.

10. Electromagnetic Waves • The sun is the ultimate source of energy that creates our weather • All radiation from the sun (electromagnetic waves), whether X-rays, radio waves, or heat waves, travel through the vacuum of space at 300,000 km/s (only slightly slower through our atmosphere) • Electromagnetic waves move outward from their source and come in a variety of sizes • The most important difference between types is their wavelength (Radio waves have the longest, and Gamma waves have the shortest) • Visible light is a small part of this electromagnetic spectrum (each color corresponds to a specific wavelength of visible light), the combination of which is white light

11. Electromagnetic Spectrum

12. Concept Check • Which electromagnetic wave has the longest wavelength? • Radio Waves

13. Radiation • Radiation – the transfer of energy (heat) through space by electromagnetic waves • Unlike conduction and convection, radiant energy can travel through the vacuum of space The four laws governing radiation • All objects, at any temperature, emit radiant energy • Hotter objects radiate more total energy per unit area than colder objects do • The hottest radiating bodies produce the shortest wavelengths of maximum radiation • Objects that are good absorbers of radiation are good emitters as well

14. Three Mechanisms of Heat Transfer

15. What Happens to Solar Radiation? • When radiation strikes an object, there usually are three different results • Some energy is absorbed by the object • Substances such as water and air are transparent to certain wavelengths of radiation • Some radiation may bounce off the object without being absorbed or transmitted

16. Reflection and Scattering • Reflection – occurs when light bounces off an object • The reflected radiation has the same intensity as the incident (coming in) radiation • Scattering – produces a larger number of weaker rays that travel in different directions • About 30 % of solar energy is reflected back into space, this energy is lost and doesn’t go into heating the atmosphere • Small particles in the atmosphere also help scatter solar radiation • About half of the solar radiation that is absorbed at Earth’s surface arrives as scattered light

17. Reflection and Scattering

18. Concept Check • How much solar energy is reflected back to space? • 30%

19. Absorption • About 50 % of the solar energy that strikes the top of the atmosphere reaches Earth’s surface and is absorbed, then is redirected skyward • Earth’s surface is continually supplied with heat from the atmosphere as well as from the sun • Greenhouse Effect – the heating of Earth’s surface and atmosphere from solar radiation being absorbed and emitted by the atmosphere, mainly by water vapor and carbon dioxide • Some incoming solar radiation is not absorbed and reradiated, but instead is used by plants for photosynthesis • Solar energy is the main energy source for virtually all life on Earth

20. Heating of the Atmosphere

21. Distribution of Incoming Solar Radiation

22. Assignment • Read Chapter 17, Section 2 (pg. 483-487) • Do Chapter 17 Assessment #1-30 (pg. 499-500) • For Section 2: #’s 5, 6, 13, 16, 20, 30