A Simple Method for Evaluating Sunshine Duration by Cloudiness Observations

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  • 1 Sogesta S.p.a., Urbino, Italy
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Abstract

A simple empirical model was set up to evaluate monthly sunshine duration on the basis of the mean daily cloudiness. A linear regression on monthly sunshine versus the number of clear, cloudy and over-cast days was fitted by a least-squares method for several years of observations at six sites in Italy, chosen as one from each 2° of latitude. Coefficients found in such a way were used to evaluate monthly sunshine duration for 16 years of observations in 35 sites well distributed over Italy. A very good agreement between observed and calculated values of hours of sunshine was found. The method seems, therefore, a suitable tool for evaluating actual sunshine in similar climates and at sites where it is not observed or to fill gaps in sets of observed data.

Abstract

A simple empirical model was set up to evaluate monthly sunshine duration on the basis of the mean daily cloudiness. A linear regression on monthly sunshine versus the number of clear, cloudy and over-cast days was fitted by a least-squares method for several years of observations at six sites in Italy, chosen as one from each 2° of latitude. Coefficients found in such a way were used to evaluate monthly sunshine duration for 16 years of observations in 35 sites well distributed over Italy. A very good agreement between observed and calculated values of hours of sunshine was found. The method seems, therefore, a suitable tool for evaluating actual sunshine in similar climates and at sites where it is not observed or to fill gaps in sets of observed data.

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