Image:Solar Spectrum.png

From Global Warming Art

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Description

This figure shows the solar radiation spectrum for direct light at both the top of the Earth's atmosphere and at sea level. The sun produces light with a distribution similar to what would be expected from a 5525 K (5250 °C) blackbody, which is approximately the sun's surface temperature. As light passes through the atmosphere, some is absorbed by greenhouse gases with specific absorption bands. Additional light is redistributed by Raleigh scattering, which is responsible for the atmosphere's blue color.

Since most of the absorption bands are located away from the peak in solar radiation, a majority (~70%) of the radiation from the sun reaches the Earth's surface. This is in contrast to the infrared radiation emitted by the Earth, whereby a majority is absorbed by bands occuring near the peak at ~5000 nm. This discrepancy, where solar light can easily reach the Earth's surface but returning energy is absorbed, is a defining quality of Earth's greenhouse effect.

These curves are based on the American Society for Testing and Materials (ASTM) Terrestrial Reference Spectra, which are standards adopted by the photovoltaics industry to ensure consistent test conditions and are similar to the light that could be expected in North America. Regions for ultraviolet, visible and infrared light are indicated.

Copyright

This figure was prepared by Robert A. Rohde.

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