## 3 Results
### MERRA-2 GDB (SSR Trends) and Its Evaluation
#### 3.2.1 Evaluation of MERRA-2 GDB (SSR Trends)
Time-series of deseasonalized anomalies of MERRA-2 and station SSR fluxes were created for each sub-period, to which a linear regression was applied and the Sen's slope and, subsequently, the trends, namely the sign and magnitude of GDB, were computed. The GDB of the reanalysis and stations is compared either on individual station or on overall (all stations) basis and the results are given in Figure S6 and Tables 2 and 3, re  
Figure 9: Agreement (blue dots) and disagreement (red dots) between trends of MERRA-2 and station deseasonalized SSR anomalies for GEBA (**a**) and BSRN (**b**) stations. The embedded white “x” symbols indicate the statistically significant trends for both MERRA-2 and stations. At the top left and top right parts above each panel figure, the numbers in parentheses provide the total number of stations for which there is agreement/disagreement (first number in parentheses) and the corresponding numbers for statistically significant trends (second number in parentheses). At the top center of each panel figure, the percent numbers of stations for which agreement, as well as those for which statistically significant agreement (in parenthesis), is found, are given. spectively, emphasizing the agreement/disagreement between the sign of the computed average GDB from all stations and the corresponding MERRA-2 pixels. Overall (Table 2), qualitative agreement in terms of the GDB sign is found for 60.6% of the GEBA stations during 1980-1985, while the corresponding percentage is equal to 49.1% for 1986-2000, 58.6% for 2001-2010 and 74.2% for 2011-2017. With respect to the BSRN stations, agreement is found for 81.8% of stations in 1992-2000, 68.2% for 2001-2010 and 63.6% for 2011-2020. This analysis allows to assess possible inter-decadal changes in terms of agreement and probable improvement with time. Thus, the comparison with GEBA initially reveals a reasonable qualitative agreement during 1980-1985, which slightly deteriorates afterwards (1986-2000) and gradually improves from 2000 on. On the contrary, the comparison with BSRN shows initially (in the 1990s) a better agreement, which gradually deteriorates after 2000. Given that an improvement of agreement with time should be expected, due to the improving quality of MERRA-2 reanalysis with time, the absence of such an improvement for BSRN stations may be attributed to the small sample of stations (22) as well as to erroneous MERRA-2 fluxes at specific sites, as discussed above. Figure 10: Agreement (blue dots) and disagreement (red dots) between trends of MERRA-2 and station deseasonalized SSR anomalies (\(\Delta\)(SSR)), for GEBA (**i-a**) and BSRN (**ii-a**) stations for the period 07/2000–06/2017. The stations showing agreement at the surface against GEBA stations (**i-a**) and BSRN stations (**ii-a**), also having agreement of \(\Delta\)(OSR) with CERES at TOA, during the same period, are shown in (**i-b**) and (**ii-b**), respectively. In the first sub-period, i.e., 1980-1985, both GEBA and MERRA-2 indicate brightening (Table 2), albeit stronger for MERRA-2 (+3.56 W/m\({}^{2}\), resulting from 156/52 pixels with brightening/dimming) than GEBA (+0.94 W/m\({}^{2}\), resulting from 107/101 stations with brightening/dimming). It should be noted that the magnitude of the average GDB is not necessarily in line with the relative number of stations/pixels exhibiting brightening and dimming. This is not strange given that the magnitude of the average GDB is also driven by the magnitude of GDB at individual stations/pixels. Yet, the obtained agreement between the signs of average MERRA-2 and GEBA GDB in the first sub-period (1980-1985) is in line with the relatively high number of stations with agreement (60.6%). In contrast, during the next two sub-periods, i.e., 1986-2000 and 2001-2010, an opposite sign of GDB is found for GEBA (brightening equal to +1.92 W/m\({}^{2}\) for 1986-2000 and +0.19 W/m\({}^{2}\) for 2001-2010) and MERRA-2 (dimming equal to \(-\)1.33 W/m\({}^{2}\) for 1986-2000 and \(-\)1.75 W/m\({}^{2}\) for 2001-2010).