'''Cloud fraction''' is the percentage of each pixel in satellite imagery or each grid box in a weather or climate model that is covered with clouds. A cloud fraction of one means the pixel is completely covered with clouds, while a cloud fraction of zero represents a totally cloud free pixel.<ref>[http://earthobservatory.nasa.gov/GlobalMaps/view.php?d1=MODAL2_M_CLD_FR Cloud Fraction] NASA Earth Observatory, January 2005.</ref> Cloud fraction is important for the modeling of downward radiation.<ref>[https://dx.doi.org/10.1016/j.rse.2012.04.006 L. Chen, G. Yan, T. Wang, H. Ren, J. Calbó, J. Zhao, R. McKenzie (2012), Estimation of surface shortwave radiation components under all sky conditions: Modeling and sensitivity analysis, ''Remote Sensing of Environment'', 123: 457–469.]</ref> Unlike sky cover, cloud fraction is often treated as the proportion of a ''horizontal area'' covered by clouds as viewed from below.<ref>{{cite journal |last1=Kassianov |first1=Evgueni |last2=Long |first2=Charles N. |last3=Ovtchinnikov |first3=Mikhail |title=Cloud Sky Cover versus Cloud Fraction: Whole-Sky Simulations and Observations |journal=Journal of Applied Meteorology |date=1 January 2005 |volume=44 |issue=1 |pages=86–98 |doi=10.1175/JAM-2184.1|doi-access=free }}</ref>
==References== {{reflist}}
Category:Numerical climate and weather models
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