## 4 Conclusions  
In this study, two recent satellite Total Cloud Cover data records (CLARA-A2 and ISCCP-H) were intercompared over the region of Europe for their coinciding years (1984-2012) and validated against surface-based observations from 22 selected stations of a European dataset of WMO stations (ECA&D). Such intercomparisons are essential for validating and assessing uncertainties in Satellite Climate Data Records ([PERSON] et al., 2016; [PERSON] et al., 2017). Both ISCCP-H and CLARA-A2 show a similar geographical pattern, however ISCCP-H has higher TCC values over lower latitudes (i.e., Mediterranean region and North Africa) and slightly lower TCC over Northern Europe. This changing pattern of differences between the two satellite TCC data sets could be attributed to the shift from geostationary to polar orbiting satellite measurements in the ISCCP-H data set, while the differences poleward of 55\({}^{\circ}\)N may be partly explained by the different number of AVHRR instruments onboard polar orbiting satellites used in the two satellite analyses. Throughout the common period of the two satellite data records, both ISCCP-H and CLARA-A2 have a similar year-to-year variability with ISCCP-H having constantly higher TCC. The aforementioned datasets have a similar seasonality with higher ISCCP-H TCC for most of the months. The validation against the ECA&D ground observations indicates a reasonable performance of the two satellite datasets. Nevertheless, CLARA-A2 is better correlated (especially over Central Europe) and less biased (in particular over Southern Europe) than ISCCP-H, with respect to ECA&D. Our results indicate a changing pattern of the comparison between the two satellite data sets and ECA&D stations with increasing latitude. More specifically, the correlation coefficients decrease with increasing latitude, above 55\({}^{\circ}\)N, while the biases improve. The improving ISCCP-H-ECA&D TCC biases could be attributed to the shift from geostationary to polar orbiting satellite measurements in the ISCCP-H data set. Although the latitudinal patterns of differences are not expected to significantly change using more stations, this deserves to be further investigated and validated in a future work. In addition, future research could focus on potential systematic differences that may appear when studying individual cloud types. Both ISCCP-H and CLARA-A2 overestimate TCC compared to ECA&D for most of the study period, resulting in overall mean overestimations of 5.2% and 2.1%, respectively. The TCC biases also vary seasonally, with maximum overestimations by CLARA-A2 in winter and by ISCCP-H in summer. Trends of both the satellite and ground-based datasets should be treated with caution because of potential artifacts due to changes in satellite configurations and their local overpass times as well as changes in ground-based instrumentation. **Supplementary Materials:** The following are available online at [[http://www.mdpi.com/2072-4292/11/2/212/s1](http://www.mdpi.com/2072-4292/11/2/212/s1)]([http://www.mdpi.com/2072-4292/11/2/212/s1](http://www.mdpi.com/2072-4292/11/2/212/s1)), Figure S1: European Geographical difference (in absolute terms) between ISCCP-H and CLARA-A2 TCC for (a) January, (b) April, (c) July and (d) October. Results are averaged over the 29-year period 1984-2012. Figure S2. Global geographical difference (in absolute terms) between ISCCP-H and CLARA-A2 TCC for (a) January, (b) April, (c) July and (d) October. Results are averaged over the 29-year period 1984-2012. Figure S3. Latitudinal dependence of the mean satellite zenith angle of CLARA-A2 and ISCCP-H over Europe (30\({}^{\circ}\)-70\({}^{\circ}\)N). For ISCCP-H two curves are plotted: the lower and upper curves show the mean satellite zenith angle at a longitude of 0\({}^{\circ}\) and 30\({}^{\circ}\)E, respectively. For latitudes larger than 50\({}^{\circ}\)N the CLARA-A2 and ISCCP-H curves overlap. Figure S4.