Image:Solar irradiance spectrum 1992.gif

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Solar_irradiance_spectrum_1992.gif‎ (13KB, MIME type: image/gif)

Spectrum of solar irradiance at top of Earth's atmosphere.

  • Neither Sun nor Earth are black bodies. Both have significant absorption by certain gases in their atmospheres, which produce absorption lines in their electromagnetic spectra, which is the distribution of energy as a function of wavelength, or wavenumber.
  • Wavenumber is the number of waves per unit length, the inverse of wavelength, and is usually given in inverse centimeters, or cm-1, with 5,000 cm-1 corresponding to a wavelength of 2 millionths of a meter, or 2 microns. Taking inverses, 10000 cm-1 is 1 micron, 20000 cm-1 is 0.5 microns, and so on to larger wavenumbers, and similarly 2000 cm-1 is 5 microns, 1000 cm-1 is 10 microns, and so on to smaller wavenumbers.
  • The distribution of energy versus wavenumber is the spectrum.

The best current estimate of the spectrum of solar irradiance at the top of the atmosphere is based on line-by-line computations by Bob Kurucz of Harvard Smithsonian Observatory. Units are Watts per square meter per inverse centimeters per steradian, and the original data has been degraded to 20 cm-1 resolution.

The red line gives the best post-1992 Solar spectum estimate, and the dark line shows the best previous estimate of the spectrum. Note the marked improvement provided by the more recent higher spectral resolution line-by-line computations. [Note that if plotted directly in wavelength, the peak would be at 0.5 microns, but a change of variables to wavenumber shifts the peak to 10000 cm-1 = 1 micron.] Common absorption lines are identified, including doubly-ionized Calcium and the first four lines of the Hydrogen Balmer series.

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Source: http://climate.gsfc.nasa.gov/~cahalan/Radiation/SolarIrr.html Author: Robert Cahalan

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  • (del) (cur) 09:24, 16 March 2005 . . SEWilco (Talk | contribs) . . 553×540 (12,785 bytes) (Spectrum of solar irradiance at top of atmosphere. {{PD-USGov-NASA}} Source: http://climate.gsfc.nasa.gov/~cahalan/Radiation/SolarIrr.html)

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