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Lecture 5

ATMO 201 Lecture Notes - Lecture 5: Negative Feedback, Positive Feedback, Ideal Gas

Atmospheric Sciences
Course Code
ATMO 201
Timothy Logan

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Lecture 5
Read appendix a pg. 463-465
Read appendix b (ideal gas, stefan-b law, and wein's law)
Thursday, January 26, 2017
3:52 PM
Atmospheric Window
Region where co2 and h2o vapor do not absorb IR radiation (8-11 um)
o Emitted LW energy passes freely into space
When clouds are present they do absorb at these wavelengths
Cirrus clouds tend to trap LW (ir) radiation
o High in atmosphere, made of ice crystals
Cumulus clouds reflect SW (UV) radiation
o Lower in atmosphere, made of water
o Can also emit IR radiation at cloud top by absorbing heat from surface
Enhancement of the Greenhouse Effect
Earth is warming - rate of .6 C per century
H2o and co2 play large roles in the warming
o Methane, nitrous oxide, and CFCs; stronger warming but much smaller roles (low
Solar radiatio oes i, ghg let i oe i ut does’t let earths radiatio leave
Climate feedbacks
Positive feedback - more warming, more water vapor released into atmosphere, more warming
Negative feedback - more water vapor, more clouds, less warming
Aerosol feedback - more aerosols, less sunlight to the surface, less warming (blocks solar radiation
from getting to the surface = cooling effect)
o Thinking about pollution, volcanoes, and wildfires
Large uncertainty in climate models
o Timing and coverage still widely contested
o Present focus on mitigation and problem solving
What happens to solar radiation?
Insolation - incident solar radiation
The fate of a solar photon
o Scattering - deflection of light indifferent directions
o Albedo - percent of solar photons reflected from a surface
Surfaces have different albedos
High albedo = you can see it like the poles
Low albedo = water and forest (you can't see it, dark colors)
R + T + A = 1
o Reflectivity - backward scattering of light
o Transmission - forward scattering of light
o Absorption - trapping of light
This is a powerful relationship!
o Reflection + absorption = extinction or loss of light
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