1. 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)

2. 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

3. Solar Spectrum = Shortwave spectrum =visible spectrum:
Sun at 6000K; peak emission at 0.5 mm

4. 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

5. Electromagnetic Spectrum
Sun
Earth
High energy
Short wavelength / high frequency
Emitted at high T

6. 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

7. Other Greenhouse Gases
water
ozone N O C H
methane
Nitrous oxide

8. Atmosphere: Characteristic Absorption/Transmission for different atm molecules for l: 0-15 µm

10. Earth Spectrum Incoming from Sun: High energy, short wavelength
0.5 mm
Outgoing from Earth
Low energy
Long wavelength
20 mm
10 mm

14. Earth’s Energy Balance50
CO2, H2O, GHG
100
Shortwave
Longwave