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