## 3 Results
### MERRA-2 GDB (SSR Trends) and Its Evaluation
#### 3.2.1 Evaluation of MERRA-2 GDB (SSR Trends)
Nevertheless, it should be noted that, actually, the disagreement for the period 2001-2010 is much weaker, and even uncertain, since the GEBA brightening is small and not significant, with values that are exceeded by the associated errors at the majority of GEBA stations (not shown here). This seems to be in line with the higher percent number (58.6%) of stations with agreement in 2001-2010 than the corresponding smaller number (49.1%) for 1986-2000. During the last sub-period, i.e., 2011-2017, both GEBA and MERRA-2 indicate dimming, which is stronger for GEBA (\(-\)1.68 W/m\({}^{2}\)) than for MERRA-2 (\(-\)0.54 W/m\({}^{2}\)). This agreement in sign of GDB is complemented by the high percent number of stations (74.2%) showing the same sign of GDB with the corresponding MERRA-2 pixels. Concerning the more problematic (in terms of agreement between the MERRA-2 and GEBA GDB) second sub-period, i.e., 1986-2000, our analysis shows (red circles in Figure S6i-b) that the overall disagreement largely arises from opposite GDB signs over Japan (disagreement in 41 out of 43 Japanese stations), a situation not found during the other three sub-periods. The reason for this disagreement can be attributed to problems with either MERRA-2 Reanalysis or the station measurements in Japan, which needs to be examined, but it is out of the scope of this study. Otherwise, no remarkable change, as it \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**GEBA Periods**} & \multirow{2}{*}{**Agreement (\%)**} & **GEBA** & **GEBA** & **MERRRA-2, pixel** & **MERRRA-2, pixel** \\  & & **\(\Delta\)(SSR) (W/m\({}^{2}\))** & **(BRL, DIM)** & **\(\Delta\)(SSR) (W/m\({}^{2}\))** & **(BRL, DIM)** \\ \hline
1980–1985 & 60.6 (75) & 0.94 & (107, 101) & 3.56 & (156, 52) \\ \hline
1986–2000 & 49.1 (47.4) & 1.92 & (161, 71) & \(-\)1.33 & (108, 124) \\ \hline
2001–2010 & 58.6 (62.5) & 0.19 & (135, 97) & \(-\)1.75 & (100, 132) \\ \hline
2011–2017 & 74.2 (80) & \(-\)1.68 & (70, 89) & \(-\)0.54 & (65, 94) \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Agreement between the GDB (\(\Delta\)(SSR)) of MERRA-2 and GEBA stations over four different time periods. The percent number of GEBA stations for which same sign of GDB is found with the corresponding MERRA-2 pixels is given (in parentheses are the statistically significant trends), along with the average \(\Delta\)(SSR) and the number of stations/pixels with brightening and dimming (shown in parentheses) for both GEBA and MERRA-2. Red and blue vectors indicate Brightening and Dimming, respectively. \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**BSRN Periods**} & \multirow{2}{*}{**Agreement (\%)**} & **BSRN** & **BSRN** & **MERRRA-2, pixel** & **MERRRA-2, pixel** \\  & & \(\Delta\)(SSR) (W/m\({}^{2}\)) & **(BRL, DIM)** & **(ASES) (W/m\({}^{2}\))** & **(BRL, DIM)** \\ \hline
1992–2000 & 81.8 (0) & 2.82 & (14, 8) & 2.08 & (14, 8) \\ \hline
2001–2010 & 68.2 (0) & \(-\)0.89 & (9, 13) & \(-\)0.08 & (8, 14) \\ \hline
2011–2020 & 63.6 (0) & 3.78 & (8, 14) & \(-\)2.43 & (6, 16) \\ \hline \hline \end{tabular}
\end{table} 
Table 3: As in Table 2, but for BSRN stations. concerns the agreement/disagreement on a regional scale, e.g., for Europe, is found from a sub-period to another. As it concerns the comparison between the MERRA-2 and BSRN GDB in different sub-periods, there is a very good agreement in the first sub-period, i.e., 1992-2000, since both of them indicate brightening, which is +2.82 W/m\({}^{2}\) for BSRN resulting from 14/8 stations with brightening/dimming and for MERRA-2 is equal to +2.08 W/m\({}^{2}\) resulting from 14/8 pixels with brightening/dimming. During the next sub-period (2001-2010), the same sign of GDB is found either for BSRN (dimming equal to \(-\)0.89 W/m\({}^{2}\)) and MERRA-2 (dimming equal to \(-\)0.08 W/m\({}^{2}\)), though both they are not statistically significant. During the last sub-period (2011-2020), an agreement is found again between the Reanalysis' and BSRN stations' GDB.