Earth 002

Thursday, January 28th, 1999
Announcements:

Lecture notes:

REVIEW ENERGY BALANCE

• Higher Temperature-->Higher Energy-->Shorter Wavelength
• E = 6(T^4)
• Distance from body greatly impacts energy received. Double distance from the sun-->1/4 energy-->Inverse Square Law [So (Ro/R)^2 = 2]
• Ein = Eout

ATMOSPHERIC COMPOSITION

• Our atmosphere is made up of nitrogen, oxygen, argon, water, and other trace elements
• Nr-->78%, O2-->21%, Ar-->9%, H2O-->varies
• Water and Carbon Dioxide interact with the atmosphere's energy
• H2O Molecules rotate in atmosphere absorbing energy in wavelengths. If absorbed at 12 microns or more, the molecule selectively absorbs any water vapor trying to leave the planet. This explains why microwaves need water when cooking b/c without the water, the heat cannot be absorbed.

• CO2 Molecules are vibrating molecules that selectively absorb energy with wavelengths of 15 microns and above. When there is symmetrical stretching. no selective absorbtion occurs. Assymetrical Stretching-->selective absorbtion at longer wavelengths around 4.5 microns.
  

GREENHOUSE EFFECT

• The greenhouse effect occurs when gases in our atmosphere selectively absorbs outgoing energy at a particular wavelength and radiates it away to heat the atmosphere
• The greenhouse effect does not act like a greenhouse
• Selective absorbers act as energy modification for earth
• S/4 (1-A) = j 6 Te^4 ---> j = 1 --> no selective absorbers, j = 0-1 --> some greenhouse effect

PROOF OF GREENHOUSE EFFECT

Balanced Energy Equaiton

Look at Energy Balance in more detail and track energy through the atmosphere to see how it is refected into our environment

• Measure the energy leaving the Earth...some wavelengths are depleted through the absorption of selective absorbers

• The atmosphere is transparent to incoming short wavelengths and opaque to outgoing long wavelengths
• Where energy is absorbed governs the temperature structure of the atmosphere