Quoted from: Dogniaux R , Lemoine M . Classification of Radiation Sites in Terms of Different Indices of Atmospheric Transparency[M]. Springer Netherlands, 1983.
https://www.sci-hub.ren/10.1007/978-94-009-7112-7_7
Systematic studies were achieved for correlating the global radiation with the relative sunshine duration and for determining the variations of their coefficients on a geographical scale as function of the radiation climatic area.
The sum A + B of the coefficients of the well - know Angstrom regression equation can be regarded as a parameter characterizing the average monthly or annual conditions of the transparency of the atmosphere at a given station. This index called "atmospheric transparency index" (ATl) is a linear function of the latitude and of the Linke turbidity factor.
A recapitulative table summarizes the different indices allowing to characterize a site. By an appropriate choice of them; it is possible to estimate with a reasonable accuracy the daily global irradiation of a site.
The aim of this study is, first, to investigate the possibility of extending the application of these equation to an extended area, by analyzing the variations of A and B as a function of latitude and atmospheric turbidity, and, in addition, to estimate the maximum values of the global radiation at the stations under clear sky conditions, by using an adequate turbidity factor well adapted to the local conditions of the site.
Dogniaux and Lemoine proposed the following correlation, where the regression coeffificients of the Angstrom–Prescott model seem to be as a function of the latitude of the site:
\( 𝐻/𝐻_0 =0.37022+[0.00506(𝑆/𝑆_0 )−0.00313]𝜑+0.32029(𝑆/𝑆_0 ) \)