Monthly specific Rietveld's correlations

Using yearly and half-yearly data Rietveld developed a method currently used to estimate monthly average daily global radiation on horizontal surfaces (H). In the present work Rietveld's method is applied to monthly data obtained for 100 European stations. The method is validated for S0/S ≲ 10, where S0 is the monthly average day length, and S is the monthly average daily sunshine duration. To estimate values of H, 12 monthly specific correlations and one correlation valid for all months are obtained for the mentioned data using Rietveld's method. Statistical comparison of monthly specific and non-specific correlations shows that relating the root mean square error, for 70% of the stations monthly specific correlations give better results than the non-specific correlations.