Clearness Index
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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 A dimensionless quantity (also known as a bare quantity, pure quantity, or scalar quantity as well as quantity of dimension one) is a quantity to which no physical dimension is assigned, with a corresponding SI unit of measurement of one (or 1) ...
and can vary from 0 (sky is completely covered) to 1 (perfectly sunny).


See also

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Cloud cover Cloud cover (also known as cloudiness, cloudage, or cloud amount) refers to the fraction of the sky obscured by clouds on average when observed from a particular location. Okta is the usual unit for measurement of the cloud cover. The cloud c ...


References

category:Atmospheric radiation {{climate-stub