12.842 / 12.301 past and present climate · ways by which the atmosphere influences climate: •...
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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.
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Climate Physics and Chemistry
Role of the Atmosphere in Climate
(Read Hartmann, Chapters 1 and 2)
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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
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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
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Image courtesy of NOAA.
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Image courtesy of NOAA.
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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.
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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.
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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
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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
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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
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Terrestrial Radiation:Effective emission temperature:
S4 0 σT a≡ − 1e p4
Earth: T K= =255 −18°Ce
Observed average surface temperature = 288K = °15 C
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Highly Reduced Model
• Transparent to solar radiation• Opaque to infrared radiation• Blackbody emission from surface and each layer
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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
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Surface temperature too large because:
• Real atmosphere is not opaque• Heat transported by convection as well as
by radiation
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Figures removed due to copyright restrictions.
See Figures in Hartmann, Dennis L. Global Physical Climatology. Reading, MA: Academic Press, p.411. ISBN: 0123285305.
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-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.