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Radiation and Energy Balance GEOG345 Sep 14 2006 Textbook: chapter 2 (2 nd half)

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Fig. 2-7, p. 35 Electromagnetic waves
Electromagnetic radiation Blackbody: emits and absorbs all possible radiation Planck’s law: the distribution of radiant energy by wavelength, as a function of temperature (T) B λ (T) = (2hc 2 / λ 5 )∙ (1/(e hc/( λ kT) -1)) B λ : radiant energy at a given wavelength k: Boltzmann’s constant; k = 1.3806503∙10 -23 ∙m 2 ∙kg∙s -2 ∙K -1 e: constant, base of the natural logarithm; e≈2.718281…. Stefan-Boltzmann law: the total radiant energy emitted E = σ T 4 σ : Stefan-Boltzmann constant; 5.670 10 -8 W m -2 K -4

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Electromagnetic radiation Wien’s displacement law: the wavelength maximum emission at a given temperature (i.e. the maximum of Planck’s function) λ max = b/T; b=2897 μ mK ≈ 3000 μ mK Sun’s surface temperature: ~6000K λ max 3000 μ mK /6000K = 0.5 µm solar or shortwave radiation Earth’s surface temperature: ~300K λ max 3000 μ mK /300K = 10 µm terrestrial or longwave radiation
Fig. 2-9, p. 37 The sun’s electromagnetic spectrum Shape: Planck’s law Wavelength of maximum radiant intensity: Wien’s law Total radiant energy: Stefan-Boltzmann law

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Fig. 2-8, p. 37 Solar vs. terrestrial radiation
visible light (blue red) 300K – typical land surface; 600K – typical smoldering; 1000K – typical flaming hot cool Black body radiation - Planck function L. Giglio

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Fig. 3, p. 38 Electromagnetic radiation With increasing distance from the source, the same amount of radiant energy is distributed over a larger area -> the radiant energy per unit area decreases.
Radiative equilibrium Rate of absorption = rate of emission No net gain / loss of energy -> no temperature change -> Radiative Equilibrium Temperature

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Earth’s radiative equilibrium temperature d SE ~150000000 km Sun Earth solar radiation (shortwave) terrestrial radiation (infrared) T s =5800K r S =696000km T E =?
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