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The Atmosphere:Part 2: Radiative equilibrium
• Composition / Structure
• Radiative transfer• Vertical and latitudinal heat transport• Atmospheric circulation• Climate modeling
Suggested further reading:
Hartmann, Global Physical Climatology (Academic Press, 1994)
S0 1367 Wm−2
Planetary energy balance
incident solar radiation incident per unit area S 0a2
4a 2 14 S0 342 Wm−2
Solar radiation absorbed per unit area 1 − pS 04 239 Wm−2
planetary albedo p ≃ 0. 30
Emitted terrestrial radiation per unit area Te4
Stefan-Boltzmann constant 5.67 10−8Wm−2K−4
Emission temperature Te S01−p
4
14 255 K
Atmospheric absorption
Principal atmosphericabsorbers
• H2O: Bent triatomic, with permanent dipole moment and pure rotational bands as well as rotation-vibration transitions
• CO2 : No permanent dipole moment, so no pure rotational transitions, but temporary dipole during vibrational transitions
• O3: Like water, but also involved in photodissociation
• Other gases: CH4, N2O, CFCs
• Clouds and aerosols
Top of atmosphere:
A ↑ Ta4
→ Ta4 1
4 1 − p S0 Te4
Te4 1 − p
S 04by definition
→ Ta Te
Bottom of atmosphere:
A ↓ Ta4 Te
4
S ↑ Ts4
→ Ts4 1
4 1 − p S0 Te4 2Te
4
→ Ts 214 Te 303 K
A more opaque atmosphere — a warmer surface
Ta = Te
T b = 21/4Te
Ts = 31/4Te
Atmospheric energy balance
Radiative equilibrium profile
Full calculation of radiative equilibrium
Full calculation of radiative equilibrium
stratosphere about right
tropospheric lapse rate too large
tropopausetoo cold
surface much too warm
Radiative equilibrium: role of various absorbers
Approach to equilibrium
Effect of clouds
Radiative effect of clouds
• Altitude and thickness
• Shape
• Liquid water content
• Ice/water
• Particle sizes