## 5 Conclusions  
The main aim of the present study was the determination of the sky status over Greece from a particular climatology point-of-view. This particularity was expressed by an analysis of the data that did not contain observations of the type of clouds and the amount of cloudiness in the sky. Instead, the study was based on an innovative methodology developed by [PERSON] [23], which uses the diffuse fraction (k\({}_{\rm d}\)) as a key parameter; in other words, k\({}_{\rm d}\) was utilised as a guideline for classifying the sky status into clear, intermediate, and overcast conditions. Such an attempt was made for the first time worldwide. Therefore, hourly values of diffuse (H\({}_{\rm d}\)) and global (H\({}_{\rm g}\)) horizontal solar irradiances at 43 sites in Greece were collected to compute the corresponding k\({}_{\rm d}\) values;  
Figure 10: Distribution of the annual mean (**a**) ASI and (**b**) AAI for clear skies over Greece derived from the TMYs of the 43 sites. The subscript CS to ASI and AAI represents clear skies. Both ASI and AAI values are dimensionless. [PERSON] [23] has defined 3 ranges of k\({}_{\rm d}\) for categorising the sky into clear, intermediate, and overcast. By counting the number of the k\({}_{\rm d}\) hourly values in each range, corresponding clear-(DCS), intermediate-(DIS), and overcast-(DOS) sky durations of sunshine were reported. The annual mean DCS, DIS, and DOS values across Greece were found to be about 1363 h, 1647 h, and 1084 h, respectively. These results were found to correspond to 33%, 40%, and 27% of the time in a year for clear-, intermediate-, and overcast-sky conditions over Greece. Linear and non-linear regression lines were fitted to the DCS, DIS, and DOS data points as function of the geographical latitude (\(\varphi\)) of the sites; negative trends were found for the first two cases and a positive one for overcast skies, as shown by the linear fits. Indeed, fewer clear-sky sunshine hours or pseudo-sunshine hours (in the case of DIS events) would be expected to occur while moving from southern to northern Greece; the opposite was found to be true for the DOS cases. On seasonal basis, the DCS events seemed to prevail in the summer, the DOS in the winter, and the DIS in the other two (transition) seasons. Such results would be expected more or less. Moreover, non-linear curves were fitted to these seasonal mean values with very good agreement with the data (R\({}^{2}\) = 1). Higher seasonal sunshine durations under clear and intermediate skies were found to occur in summer; an opposite result exits for overcast skies. The intra-annual variation in the DCS, DIS, and DOS events during the TMYs of the 43 sites showed maximum, maximum, and minimum values, respectively. The monthly mean variation in the DCS events showed a peak in July (expected as SSD\({}_{\rm CS}\), SSD for clear skies, follows the intra-annual variation in H\({}_{\rm g}\)). The monthly mean variation of the DIS events showed two peaks, one in May and another in August; the first peak may be attributed to the changing weather during the transition month of May, while the second to the almost violent thermal storms occurring near various coastal sites of Greece in the second half of August, in particular. The intra-annual fluctuation of the DOS events showed an expected clear minimum in July. Non-linear best-fitted curves were derived for the three cases, and they were found to vary well-within their \(\pm\)10 band. According to [PERSON] [23], k\({}_{\rm d}\) could be interpreted as an atmospheric scattering index (ASI). In order to investigate the influence of ASI on the sky status of Greece, the intermediate-sky range was divided further into three smaller sub-ranges, i.e., DIS-1 where clear-sky conditions and fast-moving clouds prevail, DIS-2 with prevailing cirrus, fast-moving or low-level clouds, and DIS-3 with prevalence of thicker clouds.