## 4 Conclusions  
The present study estimated the Linke (\(T_{\rm L}\)) and Unsworth-Monteith (\(T_{\rm UM}\)) turbidity parameters at 33 sites in Greece under all and clear-sky conditions over a year. That year was considered typical (Typical Atmospheric Turbidity Year, TATY) because the estimation of both turbidity factors was based on values of the meteorological parameters that comprise recently-derived Typical Meteorological Years for the same sites. Each TATY consists of the same TMMs as in the TMYs-PV for the specific location. The present work presented some innovations: (i) the notion of TATY was introduced for the first time worldwide; (ii) turbidity-parameter maps for Greece were derived for the first time; (iii) the definition of the modified diffuse fraction was introduced for the first time worldwide; and (iv) use of the climatic zones of Greece for energy purposes was made, since atmospheric turbidity is used in advanced solar codes to estimate solar radiation at a location destined for energy applications (e.g., PV installations). For the sake of simplicity, two representative sites per climatic zone were selected in some parts of the analysis. Month-hour graphs for \(T_{\rm L}\) and \(T_{\rm UM}\) were prepared for the eight selected sites. For all-sky conditions, relatively high values of \(T_{\rm L}\) were found in the mornings and evenings during January-March or even early April; lower values were found in the other months of the year. The \(T_{\rm UM}\) variation indicated a similar pattern to that of \(T_{\rm L}\) with a slight differentiation because of the dependence of \(T_{\rm UM}\) on the water vapor in the atmosphere. Under clear skies, the \(T_{\rm L}\) month-hour graphs showed a pattern resembling the all-sky pattern. The morning and evening peaks were retained in the period January-March, with maximum values in the morning hours throughout the year, but these were lower than those in late winter-early spring. In the evening (late spring-early winter), the \(T_{\rm L}\) values were lower than the morning values. \(T_{\rm UM}\) followed the \(T_{\rm L}\) pattern as in the case of all skies. Similar patterns were found for the other 25 sites, but they were not shown in the study for space-saving reasons. The intra-annual variation of both parameters showed a pattern with maximum values in early spring and late summer and lower values in summertime and most winter months. This behavior was found to be consistent with the intra-annual variation of the turbidity factors at other sites in Europe and Africa. Maps of the annual mean values of the turbidity parameters over Greece for all and clear-sky conditions were prepared. Persistent low values were found over Peloponnese all over the year and higher values in the southern part of the Ionian Sea. Because of the difficulty in estimating \(T_{\rm UM}\) (i.e., more elaborate calculations than for \(T_{\rm L}\); compare methodologies in Sections 2.1.1 and 2.1.2), linear expressions with high coefficients of determination (R\({}^{2}\)) were given for \(T_{\rm UM}\) as function of \(T_{\rm L}\) for all sites and both all and clear-sky conditions. Finally, an attempt to facilitate the estimation of the diffuse horizontal solar radiation at any location in Greece was made, if the global horizontal radiation is known or can be estimated via a solar code. Linear expressions of \(k^{\prime}_{\rm d}\) vs. \(k^{\prime}_{\rm t}\) were derived for the sites in each climatic zone as well as for all sites regardless of zone. The expressions provided high values of R\({}^{2}\), thus showing their applicability. Conceptualisation, methodology, data collection, data analysis, and writing--original draft preparation, H.D.K. ; methodology, mathematical formulation, review and editing, B.E.P. All authors have read and agreed to the published version of the manuscript. This research was implemented in the frame of the KRIPIS-THESPIA-II project, grant number MIS 5002517, funded by the General Secretariat of Research and Technology in Greece.