03RadiationCirculation

03RadiationCirculation - ESM 203: Energy balance and...

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ESM 203: Energy balance and ESM 203: Energy balance and atmospheric circulation atmospheric circulation Jeff Dozier & Thomas Dunne Fall 2007 1
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Solar radiation at top of at top of atmosphere atmosphere (MJ m –2 –2 day day –1 –1 ) Dingman, Figure 3-6 2
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3 Wavelengths of radiation and the atmosphere Wavelengths of radiation and the atmosphere Ultraviolet (<0.4 μ m): absorbed by stratospheric ozone (less ozone more UV) Visible (0.4–0.7 m): scattered by air molecules, dust, soot, salt, clouds Scattering by air greater for shorter wavelengths (blue). Near-infrared (0.7-3.0 m) (from Sun): scattered less, but absorbed by water vapor, especially at 1.4 and 1.9 μ m, and by clouds Middle infrared (3-5 m) (from Sun and Earth) and thermal infrared (>5 m) (from Earth): absorbed by clouds, water vapor, carbon dioxide, methane, ozone, and other “greenhouse” gases Some “windows” (3.5-4.0 μ m and 10.5-12.5 μ m) when no clouds
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0 50 100 150 200 250 300 0 0.2 0.4 0.6 0.8 1 Albedo Temperature (K) The simplest climate model—energy The simplest climate model—energy balance with a non-absorbing balance with a non-absorbing atmosphere atmosphere Solar radiation absorbed by whole Earth = infrared radiation emitted by whole planet i.e., net all-wave radiation = 0 S 0 = solar radiation α = planetary average albedo F F = infrared radiation T = planetary surface temperature ε 0.90-0.95, σ = 5.67×10 8 S 0 = 1370 W m –2 normal to Sun Divide by 4 to average over Earth, 342.5 Wm –2 Albedo 0.27-0.33 (see Charlson) Thus T 255 ° K = –18 ° C ( 29 ( 29 4 / 1 0 4 1 4 , so 1 4 - = = = - α εσ S T T F S o 4
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Interpretation Interpretation If the atmosphere didn’t absorb radiation, the global average temperature should be about – 18 ° C. Near the surface, average air temperature is measured to be about 16 ° C. The discrepancy must be due to the role of the atmosphere in absorbing energy and storing it near the surface. This interaction between solar radiation and the atmosphere begins the processes of energy transfer that create climate 5
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Variation of atmospheric temperature with elevation Variation of atmospheric temperature with elevation reflects absorption of radiation emitted from surface and reflects absorption of radiation emitted from surface and absorbed by atmospheric gases absorbed by atmospheric gases Graedel, T. E. and P. J. Crutzen (1995) Atmosphere, Climate and λ < 0.1 μ m absorbed by N 2 , O 2 , N, O λ < 0.2 μ m absorbed by O 2 O 3 absorbs λ < 0.31 μ m and λ ~8 μ m λ > 0.31 μ m warms surface, which radiates and warms atmosphere 6
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Most of the atmospheric Most of the atmospheric constituents that absorb out- constituents that absorb out- going long-wave radiation (relatively large asymmetric (relatively large asymmetric molecules) although natural, are augmented by pollutant are augmented by pollutant gases.
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This note was uploaded on 08/06/2008 for the course ESM 203 taught by Professor Dozier,dunne during the Fall '07 term at UCSB.

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03RadiationCirculation - ESM 203: Energy balance and...

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