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Published byJuliet Cain Modified over 9 years ago
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Language of the Energy Cycle: The Electromagnetic Spectrum
Wavelength l Speed of light = wavelength (l) x frequency = 3 x 108 m/s in vacuum Wavenumber = 1/ wavelength ( cm-1) Frequency in GHz (1 Hz = sec –1)
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1. Power Source: Blackbody Radiation
Planck’s Law: The amount and spectrum of radiation emitted by a blackbody is uniquely determined by its temperature Max Planck (1858 – 1947) Nobel Prize 1918 620 K 380 K Emission from warm bodies peak at short wavelengths wavelength
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Solar Spectrum = Shortwave spectrum =visible spectrum:
Sun at 6000K; peak emission at 0.5 mm
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Terrestrial Spectrum = Longwave Spectrum = Infrared Spectrum = Thermal Spectrum: Sahara Desert on Nimbus 4 Satellite CO2 H2O O3 Theoretical Planck curves: Earth ~300K, peak emission ~15 mm
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Electromagnetic Spectrum
Sun Earth High energy Short wavelength / high frequency Emitted at high T
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Vibrational Modes for CO2
2. What happens to the radiation in the atm? Vibrational Modes for CO2 C O n1 symmetric n bending 15 mm n2 asymmetric 4.3 mm Greenhouse effect: Radiation at specific wavelengths excite CO2 into higher energy states: energy is “absorbed” by the CO2 molecules
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Other Greenhouse Gases
water ozone N O C H methane Nitrous oxide
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Atmosphere: Characteristic Absorption/Transmission for different atm molecules for l: 0-15 µm
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Earth Spectrum Incoming from Sun: High energy, short wavelength
0.5 mm Outgoing from Earth Low energy Long wavelength 20 mm 10 mm
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Earth’s Energy Balance
50 CO2, H2O, GHG 100 Shortwave Longwave
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