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MIT OpenCourseWare http://ocw.mit.edu
12.842 / 12.301 Past and Present ClimateFall 2008
For information about citing these materials or our Terms of Use, visit: http://ocw.mit.edu/terms.
Climate Physics and Chemistry
Role of the Atmosphere in Climate
(Read Hartmann, Chapters 1 and 2)
Ways by which the atmosphere influences climate:
• Strong effects on radiative transfer, including filtering of ultraviolet radiation
• Large advective and convective heat transfer
• Main driver of ocean circulation• Important role in biogeochemical cycles
0.000004%O3*Ozone
0.00003%N2O*Nitrous Oxide
0.00005%H2Hydrogen
0.00017%CH4*Methane
0.0005%HeHelium
0.0018%NeNeon
0.0360%CO2*Carbon Dioxide
0.93%ArArgon
0 to 4%H2O*Water
20.95%O2Oxygen
78.08%N2Nitrogen
Percent VolumeChemical FormulaGas Name
Atmospheric Composition
* variable gases
Image courtesy of NOAA.
Image courtesy of NOAA.
0-100
Troposphere
Tropopause
Stratosphere
StratopauseMesosphere
Mesopause
Thermosphere
-80 -60 -40 -20 0 20
10000
20000
30000
40000
50000
60000
Alti
tude
(met
ers)
Temperature oC
70000
80000
90000
100000
Figure by MIT OpenCourseWare.
Figures removed due to copyright restrictions.
See Figure 1.6 and Figure 1.7 in Hartmann, Dennis L. Global Physical Climatology. Reading, MA: Academic Press, p.411. ISBN: 0123285305.
Elements of Thermal Balance:Solar Radiation
• Luminosity: 3.9 x 1026 J s-1 = 6.4 x 107 Wm-2
at top of photosphere
• Mean distance from earth: 1.5 x 1011 m• Flux density at mean radius of earth
L0 −2S W≡ =1370 m0 24πd
Stefan-Boltzmann Equation: F T=σ 4−8 − −2 4σ = ×5.67 10 Wm K
4 27 −Sun: σT W= ×6.4 10 m→ T K6,000
Disposition of Solar Radiation:
( )
2Total absorbed solar radiation = −S a 1 π r0 p pa ≡ planetary albedo 30%p
2Total surface area = 4π rpS0 Absorption per unit area = − 1 a4 p
Absorption by clouds, atmosphere, and surface
Terrestrial Radiation:Effective emission temperature:
S4 0 σT a≡ − 1e p4
Earth: T K= =255 −18°Ce
Observed average surface temperature = 288K = °15 C
Highly Reduced Model
• Transparent to solar radiation• Opaque to infrared radiation• Blackbody emission from surface and each layer
Radiative Equilibrium:Top of Atmosphere:
S4σ 0 T a= − 1 = TA 4 p e
Surface:SσT T4 4 0 ( )1 2 4
s = +σ A p− a = T4
→ =T TA e
4σ
σ e
1→ =T Ts e2 34 = 03 K
Surface temperature too large because:
• Real atmosphere is not opaque• Heat transported by convection as well as
by radiation
Figures removed due to copyright restrictions.
See Figures in Hartmann, Dennis L. Global Physical Climatology. Reading, MA: Academic Press, p.411. ISBN: 0123285305.
-90 -6
-4
-2
0
2
4
6
-60 -30 Latitude
0 30 60 90
Atmosphere
Heat Transport by Oceans and Atmosphere
peta
Wat
ts
Ocean Transport
Total Transport Transport
Figure by MIT OpenCourseWare.