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However, about half the direct beam radiation blocked by cumulus clouds is
recovered in the form of diffuse radiation. Cirrus, or wispy, high altitude clouds, are
not as effective in blocking sunlight, and about two thirds of the direct beam radiation
blocked is converted to diffuse radiation. On a totally cloudy day, with no sunshine,
most radiation reaching the earth’s surface will be diffuse (Liu & Jordan, 1960).
Figure 1.7. Atmospheric scattering leading to diffuse radiation.
Figure 1.8. The effect of cloud cover on radiation reaching the earth’s surface.
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