The clearness index is a measure of atmosphere clearness. It is calculated as the fraction of the actual total
solar radiation
Solar irradiance is the power per unit area (surface power density) received from the Sun in the form of electromagnetic radiation in the wavelength range of the measuring instrument.
Solar irradiance is measured in watts per square metre ( ...
on the surface of the Earth during a certain period over the theoretical maximum (clearsky) radiation during the same period. The clearness index is a
dimensionless quantity and can vary from 0 (sky is completely covered) to 1 (perfectly sunny).
See also
*
Cloud cover
References
category:Atmospheric radiation
{{climate-stub