## 3 Results  
### Climatologies and Differences of CLARA-A2 and ISCCP-H  
Average values of the TCC were calculated for the European region for the 29-year period of 1984-2012, which is the common period for the two satellite data records, CLARA-A2 and ISCCP-H. The selected study region extends from 30\({}^{\circ}\)N to 70\({}^{\circ}\)N and from 10\({}^{\circ}\)W to 30\({}^{\circ}\)E, and includes areas of distinct geomorphology characterized by diverse climatic regimes, ranging from the Mediterranean to oceanic, continental and sub-Arctic, thus encompassing different cloud regimes. Figure 2a,b shows the overall mean TCC for CLARA-A2 and ISCCP-H. The general geographical pattern regarding the two satellite data sets appears quite similar, with a gradual increase in cloud cover from the South to the North-West. Minimum values for both data records are located over the region of North Africa and the South Mediterranean basin with cloud cover values of approximately 25% and 30% for CLARA-A2 and ISCCP-H respectively. Moreover, the two satellite data records present the maximum TCC values to the North of the United Kingdom and North-West of Norway (Norwegian Sea). For CLARA-A2 the absolute maximum is slightly larger than that of ISCCP-H. The absolute differences between ISCCP-H and CLARA-A2 TCC, shown in Figure 2c, indicate that apart from the similarity in spatial patterns, there is a good quantitative agreement between the two data records over a significant part of the study region (covering almost the entire continental Europe) with differences less than 2.5% in absolute terms. However, a greater contrast can be observed over the Mediterranean Sea and North Africa where ISCCP-H has higher TCC in comparison to CLARA-A2 (reddish colors). Specifically, the magnitude of differences varies from 5% to 10% for most of the Mediterranean basin, with an absolute maximum of approximately 15% over the Aegean Sea. Secondarily, large TCC differences (larger ISCCP-H than CLARA-A2 values) between the two satellite datasets appear off the western coasts of the Iberian Peninsula and France. In contrast, ISCCP-H TCC values are smaller than CLARA-A2 over the northernmost part of the study region, namely over areas with higher latitude than 65\({}^{\circ}\)N, mainly over the Scandinavian countries and to the northwest of Norway where absolute differences range from approximately -2.5% to -7.5%. Similar findings, namely larger ISCCP-H than CLARA-A2 TCC over the southernmost parts of the study region and lower ISCCP-H TCC over its northernmost parts, are shown by [PERSON] and [PERSON] 2018 (Figure 1) [50] also in nearby regions. Moreover, our results in Supplementary Figures S1 and S2 show that the differences in the northernmost parts exist throughout the year and those in the southernmost ones are apparent in all seasons except winter. \begin{table}
\begin{tabular}{c c c} \hline
**ECA\&D Station** & **Latitude** & **Longitude** \\ \hline _Geneve-Observatoire (10)_ & 46.25\({}^{\circ}\)N & 06.13\({}^{\circ}\)E \\ _Lugano (11)_ & 46.00\({}^{\circ}\)N & 08.97\({}^{\circ}\)E \\ _Zagreb-Gric (12)_ & 45.82\({}^{\circ}\)N & 15.98\({}^{\circ}\)E \\ _Belgrade (13)_ & 44.80\({}^{\circ}\)N & 20.47\({}^{\circ}\)E \\ _A Coruha (14)_ & 43.37\({}^{\circ}\)N & 08.42\({}^{\circ}\)W \\ _Bilbao-Aeropuerto (15)_ & 43.30\({}^{\circ}\)N & 02.91\({}^{\circ}\)W \\ _Zaragoza-Aeropuerto (16)_ & 41.66\({}^{\circ}\)N & 01.01\({}^{\circ}\)W \\ _Barcelona-Aeropuerto (17)_ & 41.29\({}^{\circ}\)N & 02.07\({}^{\circ}\)E \\ _Madrid-Barajas (18)_ & 40.47\({}^{\circ}\)N & 03.56\({}^{\circ}\)W \\ _Corfu (19)_ & 39.62\({}^{\circ}\)N & 19.92\({}^{\circ}\)E \\ _Athens-Hellinikon (20)_ & 37.90\({}^{\circ}\)N & 23.75\({}^{\circ}\)E \\ _Sevilla-San Pablo (21)_ & 37.42\({}^{\circ}\)N & 05.88\({}^{\circ}\)W \\ _Heraklion (22)_ & 35.33\({}^{\circ}\)N & 25.18\({}^{\circ}\)E \\ \hline \end{tabular}
\end{table}