## 3 Results
### MERRA-2 GDB (SSR Trends) and Its Evaluation
#### 3.2.2 The MERRA-2 GDB on Global, Hemispherical and Regional Scales  
The global distribution of MERRA-2 GDB, i.e., \(\Delta\)(SSR), over the 40-year period 1980-2019 is given in Figure 11. Note that in this part of the analysis, which does not include comparison against stations, MERRA-2 data for 40 (instead of 37) years were utilized, since there is no restriction caused by the availability of GEBA/BSRN stations data. The computed \(\Delta\)(SSR) values resulted from the application of linear regression to the time series of deseasonalized monthly MERRA-2 SSR anomalies for each pixel and the computation of the Sen's slope. Information about the statistical significance of GDB is also provided in the same figure (dotted colored pixels). According to MERRA-2, strong and statistically significant brightening (up to +32.9 W/m\({}^{2}\) or +0.826 W/m\({}^{2}\)/year) is found over Europe, Central Africa, Mongolia, Mexico and some parts of the Tropical oceans, of Brazil and Argentina. In contrast, strong and statistically significant dimming (as strong as \(-\)57.38 W/m\({}^{2}\) or \(-\)1.435 W/m\({}^{2}\)/year) is found over the western Tropical Warm Pool, India, Southeast China, Amazonia, starcumulus covered areas and some parts of oceans such as over the mid-latitude Southern Hemisphere Ocean. No statistically significant trends were found over extended areas such as North America, Russia, Australia, Japan and Western Sahara. Opposite trends of SSR are found in neighboring areas over Africa, North and South America, Australia, Southeast Asia, eastern Tropical Warm Pool and the Mediterranean. Overall, solar dimming dominates (dimming in 62.8% of pixels versus brightening in 37.2% of pixels). According to our results, the computed tendencies of MERRA-2 SSR are statistically significant in 57% of pixels all over the globe; in those cells, i.e., over global areas with statistically significant GDB, solar dimming dominates even more, occurring in 81% of them. The overall dimming arises from global oceans (brightening/dimming in 27.7%/72.3% of pixels), while brightening slightly dominates over land (brightening/dimming occurring in 56.5%/43.5% of pixels). Additional information about the MERRA-2 GDB obtained on a seasonal basis (Figure S7) reveals seasonal variation of GDB features on a regional basis. For example, the annual brightening identified over Europe (Figure 11) is driven by a strong brightening in March-April-May and June-August, while a weaker brightening occurs in September-November, and mixed patterns are observed in December-February. Over the Southern Ocean, the stratocumulus-covered ocean areas off the western coasts of South Africa and America, the Tropical Warm Pool, Amazonia and India, a systematic dimming is observed throughout the year, resulting in an annual dimming over these areas. Moreover, the dimming observed on an annual basis over Sahara (Figure 11), arises from a dimming throughout the year, being strongest in June-August, except for December-February when brightening occurs. Figure 12 displays the time series of the computed average deseasonalized SSR anomalies for the Globe, Northern Hemisphere and Southern Hemisphere over the 40-year period January 1980-December 2019. The MERRA-2 hemispherical SSR anomalies range from \(-8\) to \(10.52\) W/m\({}^{2}\), while the global mean SSR anomalies vary up to \(6.33\) Wm\({}^{-2}\). Large positive anomalies (brightening) are found during 1980-1991, while systematic negative anomalies, i.e., dimming, are observed during 2003-2019. This leads to an overall strong negative trend over the entire 1980-2019 period either over the Globe and the two hemispheres. Stronger positive anomalies occur in the SH than in the NH during 1980-1991, while after the Pinatubo eruption (1991) and through to 2019 larger negative anomalies occur again in the SH than in the NH. The 4 th-order polynomial fit applied to the 40-year time-series shows a stronger decline of SSR during the period 1991-2008, against a stabilizing tendency of SSR afterwards.