The Azimuth Project
Solar radiation (Rev #2, changes)

Showing changes from revision #1 to #2: Added | Removed | Changed

Solar output

Solar output

The total solar output to space is 3.84 ×\times 1024 watts, but only a tiny fraction hits the Earth. At the top of the atmosphere, energy is received with a flux, or power density of 1366±\pm2 W/m2, a value known as the solar constant. About 7% is ultraviolet (wavelength 0.2-0.4μ\mum), 41% visible light (0.4-0.7μ\mum) and 51% near-infra-red (>\gt 0.7μ\mum).

Because the radiation hits the earth’s Earth at an angle, and not at all at night, the average global power density is 342W/m2 at the top of the atmosphere. (This is one quarter of 1366 W/m2, since the area of a sphere is four times the area of its circular shadow.)

Surface receipt of solar radiation

Surface receipt of solar radiation

About 18% of the incoming energy is absorbed directly by ozone and water vapour. This almost entirely removes wavelengths shorter than 0.285μ\mum while those longer than 0.295μ\mu m reach the ground. About 30% of incoming solar radiation is reflected directly back into space by the atmosphere, clouds, and the earth’s surface, surface. leaving The remaining 70% to heats heat the surface (approx (approximately 50%) 50% goes there) and atmosphere (approx (approximately 20%). 20% goes there).

The earth’s surface receives 156W/m2 from the sun (as a global average) and emits 55W/m2 long-wave energy to the atmosphere. The atmosphere receives 84W/m2 and emits 185W/m2 to space. (The figures here are from Barry and Chorley, 2003. The account in Kiehl and Trenberth’s paper is more complicated.)

The figures in the last para are from Barry and Chorley, 2003. The Kiehl and Trenberth account is more complicated.

References

References

  • R. G. Barry and R. J. Chorley, Atmosphere, Weather and Climate, Routledge, London, 2003.

  • J. T. Kiehl and Kevin E. Trenberth, Earth’s annual global mean energy budget, Bull. Amer. Meteor. Soc. 78 (1997), 197–208.

Atmosphere, Weather and Climate, R G Barry and R J Chorley, Routledge 2003

J. T. Kiehl and Kevin E. Trenberth, Earth’s Annual Global Mean Energy Budget, 1997, Bull. Amer. Meteor. Soc., 78, 197-208.