## 3 Results
### Trends  
#### 3.3.1 SSR Trends  
To gain insight into the SSR changes during the fifteen-year period (2005-2019), trends are calculated for each one of the 16 locations, as described in detail in Section 2.2.3. The trends of the SSR values produced by our system (SBDART), from the CM SAF SARAH-2.1 (2005-2017) and the CERES EBAF edition 4.1 satellite-based products, and from the two ground stations (Athens and Thessaloniki) covering the whole time period, appear in Figure 8. The SSR timeseries, along with the trends and relative trends (trends relative to the first year, as in [PERSON] et al. [27]), and the corresponding uncertainties (\(\pm 1\sigma\)) for each station, are shown in Figures 9-11, correspondingly.  
It is shown, in Figure 8a and Table 3, that positive SBDART SSR trends ranging from 0.01 (Rhodes) to 0.52 W/m\({}^{2}\)/year (Olympus) appear over all the locations except for two, which are Mytilene (\(-0.27\) W/m\({}^{2}\)/year or \(-0.14\%\)/year) and HCMR (\(-0.12\) W/m\({}^{2}\)/year or \(-0.06\%\)/year). Only over the two locations with the strongest trends, Volos (0.78 W/m\({}^{2}\)/year or 0.45%/year) and Thessaloniki (0.67 W/m\({}^{2}\)/year or 0.40%/year), are the trends statistically significant at the 95% confidence level. The SBDART SSR trends, in general, agree with those of CM SAF (Figure 8b) and CERES (Figure 8c). Differences in the magnitude of the trends are expected, due to the special characteristics of the satellite-based products (sensors with different spatial and temporal resolution), and the different methods and assumptions involved in the calculations.  
Our SBDART SSR trends are in better agreement with the CERES trends than the CM SAF. Apart from the slightly different period (2005-2017) covered by the CM SAF data, it is also well known that this product is based on climatological aerosol data [18], and hence misses the trends induced by aerosols compared to our SBDART SSR and CERES (both use MODIS aerosol data). On the other hand, due to its high spatial (0.05\({}^{\circ}\)\(\times\) 0.05\({}^{\circ}\)) and temporal (30 min) resolution, this product probably obtains a better representation of cloud radiative effects [27]. The CERES EBAF edition 4.1 product also incorporates cloud information from geostationary satellites, and the radiative calculations are resolved on an hourly basis. However, its low spatial resolution (1\({}^{\circ}\)\(\times\) 1\({}^{\circ}\)) will definitely impact the trend calculations.  
Compared to the ground-based observations from Athens and Thessaloniki, it is shown, in Figure 8d and Figure S12, that the strong positive SSR trend over Athens (0.66 W/m\({}^{2}\)/year or 0.34%/year) is captured better by our SBDART SSR than CM SAF and CERES, but, contrary to the ground-based trends, statistical significance is not indicated. Over Thessaloniki, ground-based observations exhibit a statistically insignificant positive trend (0.26 W/m\({}^{2}\)/year or 0.14%/year), which is better captured by CERES compared to SBDART and CM SAF. The evaluation of the SSR trends against the data from two ground stations only does not allow for safe conclusions; however, it is pretty enhancing that all the three independent datasets capture the sign of the trends.