lecture 19 - 4/16/2011 Solar Radiation Solar Radiation...

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4/16/2011 1 Solar Radiation Solar Radiation Solar Radiation • The sun is a nearly spherical source of radiation whose outer diameter is 1.39 x 10 9 m and whose emissive power approximates that of a blackbody at 5800 K . • The distance from the center of the sun to the center of the earth varies with time of year from a minimum of 1.471 x 10 11 m to a maximum of 1.521 x 10 11 m, with an annual average of 1.496 x 10 11 m. • Due to the large sun-to-earth distance, the sun’s rays are nearly parallel at the outer edge of the earth’s atmosphere, and the corresponding radiation flux is x Sc qf S   2 the or heat flux 1353 W/m when the earth is at its mean dist solar cons ance from th ta e nt sun. c S
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4/16/2011 2 Solar Radiation (cont). • Interaction of solar radiation with earth’s atmosphere: Absorption by aerosols over the entire spectrum. Absorption by gases (CO 2 , H 2 O ( ), O 3 ) in discrete wavelength bands. v Scattering by gas molecules and aerosols .
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4/16/2011 3 Solar Radiation (cont). Effect of Atmosphere on Spectral Distribution of Solar Radiation: Attenuation over the entire spectrum but more pronounced in spectral bands associated with polar molecules. Terrestrial Radiation Terrestrial Radiation Emission by Earth’s Surface : 4 ET  Emissivities are typically large. For example, from Table A.11: Sand/Soil: 0 90 Water/Ice: 0 95 Vegetation: 0 92 Snow: 0 82 Concrete/Asphalt: 0 85 . . . . . Emission is typically from surfaces with temperatures in the range of 250 < T < 320 K and hence concentrated in the spectral region with peak emission at 44 0 m ,  10 m . Atmospheric Emission : Largely due to emission from CO 2 and H 2 O (v) and concentrated in the spectral regions 5 8 m and 13 m . 
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4/16/2011 4 Terrestrial Radiation (cont). Although far from exhibiting the spectral characteristics of blackbody emission, earth irradiation due to atmospheric emission is often approximated by a blackbody emissive power of the form 4 atm sky GT effective sky te mperatu e t r e h sky T 230 K< 285 K sky T Cold, clear sky Warm, overcast sky
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This note was uploaded on 05/18/2011 for the course MEEG 342 taught by Professor Staff during the Spring '08 term at University of Delaware.

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lecture 19 - 4/16/2011 Solar Radiation Solar Radiation...

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