Key topics and questions for review

  • Climate System. Where is the energy driving the Earth's atmospheric circulation and ocean currents derived originally from?
  • A significant process of atmosphere heat transfer is radiation -- the transfer of energy by means of electromagnetic waves.
  • Absolute zero: Temperature of - 273.15 degrees Celsius. At this temperature atomic motion stops.
  • All objects with a temperature above absolution zero emit radiation at a rate proportional to the fourth power of their absolute temperature.
  • The higher an object's temperature, the greater the amount of radiation emitted per unit surface area and the shorter the wavelength of maximum emission.
  • Visible light has wavelengths between 0.4 and 0.8 micrometer, and dominates solar radiation output.
  • The sun behaves as a blackbody, which can be defined as any object which both absorbs and emits radiation with maximum efficiency.
  • The earth's surface behaves as a blackbody, making it a much better absorber and emitter of radiation than the atmosphere. (This latter part will be explained further in next lecture.)
  • The energy output of any blackbody radiator can be calculated from its temperature using the Stefan-Boltzmann Law (i.e., page 36 in Ahrens' book) .
  • Solar constant -- At the top of the atmosphere, solar energy received on a surface perpendicular to the sun's rays appears to remain fairly constant at nearly two calories on each square centimeters each minute or 1367 Watts per square meter -- a value called the solar constant. [Note that solar "constant" changes with time, see Figure 19.15, pages 534-535 in Ahrens' book. Solar constant varies by only about 0.1% over an 11-year sunspot cycle.]
  • Planetary albedo -- the Earth and its atmosphere behave like a partial mirror, and reflect about 31% of the incoming solar radiation back to space. This amount is termed the planetary albedo.
  • Whereas the hot sun emits the majority of its radiation between at wavelengths less than 2 μm [with maximum radiation near 0.5 μm],  the relatively cool earth emits almost all of its energy at wavelengths between about 5-25 μm [with maximum radiation near 10 μm].
  • The earth absorbs solar radiation only during the daylight hours; however, it emits infrared radiation continuously, both during the day and at night.
  • Over the earth as a whole, outgoing infrared energy equals incoming solar energy. [Also called radiative equilibrium]
Additional Readings:
Last updated on 01/05/10 03:25 PM