# Comparison of SEVIRI-Derived Cloud Occurrence Frequency and Cloud-Top Height with A-Train Data
## 3 Results  
### Cloud Occurrence Frequency  
Table 2 summarises all of the matchup results for individual months for the mean COFs for CPR, CALIOP, and SEVIRI cloud products; bias scores of SEVIRI against CPR and CALIOP products; and the numbers of co-located data used to calculate the validation scores. It should be noted that the numbers of co-located data in January and February 2014 were relatively small owing to the outage of Meteosat-10 for scheduled decontamination on 14-21 January 2014, in addition to a data collection failure for this study during that period. Most of the matchup data were collected from the SEVIRI observation area with a higher satellite zenith angle because of the collocation time calculation fault; thus, the scores do not have strong consistency and should be interpreted carefully. The bias score clearly shows that CALIOP estimated a greater COF of 61.23% for the comparison period from May 2013 to April 2014. In addition, CPR detected a significantly lower COF of 42.98%, and SEVIRI COF was in the middle but was closer to that of CALIOP with a value of 57.33%. That is, CALIOP showed a COF 3.90% higher (in absolute terms) than that derived for SEVIRI, whereas CPR showed a COF 14.35% lower than that for SEVIRI. On the seasonal variation of monthly-mean COFs, a trend is apparent in all three products such that COFs increased in the boreal winter and early spring and decreased in the boreal summer over the Meteosat-10 observation area, where December-February (June-August) represents boreal winter (summer). The monthly-mean COFs of CPR, CALIOP, and SEVIRI varied within 9% from 37.01 to 46.04, 13% from 53.20 to 66.19, and 9% from 51.39 to 60.51, respectively, when ignoring January and February due to the statistical insignificance. CALIOP showed slightly larger seasonal variability. The bias of the SEVIRI COF was from 13.09 to 15.89 compared with the CPR and from \(-\)5.68 to \(-\)1.57 for CALIOP. To investigate the COF tendency with regard to the surface type, we computed the scores over land and ocean separately (Table 3). About 64% of the derived matchup dataset corresponded to ocean pixels, with the remainder over land surfaces. All COFs showed larger values over the ocean. The differences of COFs with respect to the surface type were about 7%-11% for the CPR and the CALIOP products, increasing to about 20% for SEVIRI. The SEVIRI product even showed a positive bias over the ocean compared with CALIOP in the monthly statistics for most months except for \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{**Year**} & \multirow{2}{*}{**Month**} & \multicolumn{2}{c}{**Mean Cloud Occurrence (\%)**} & \multicolumn{2}{c}{**SEVIRI Bias (\%)**} & \multirow{2}{*}{**Number of Data**} \\ \cline{3-3} \cline{5-8}  & & **CPR** & **CALIOP** & **SEVIRI** & **CPR** & **CALIOP** \\ \hline \multirow{8}{*}{2013} & May & 43.39 & 61.70 & 57.32 & 13.93 & \(-\)4.38 & 68162 \\  & June & 38.85 & 57.31 & 53.25 & 14.40 & \(-\)4.06 & 59384 \\  & July & 37.01 & 53.20 & 51.39 & 14.38 & \(-\)1.81 & 77620 \\  & August & 40.67 & 58.13 & 56.56 & 15.89 & \(-\)1.57 & 82891 \\  & September & 40.69 & 58.76 & 55.68 & 14.99 & \(-\)3.08 & 72390 \\  & October & 42.16 & 61.85 & 57.36 & 15.20 & \(-\)4.49 & 67751 \\  & November & 44.14 & 61.93 & 58.46 & 14.32 & \(-\)3.47 & 82263 \\  & December & 45.12 & 66.19 & 60.51 & 15.39 & \(-\)5.68 & 97163 \\ \hline \multirow{4}{*}{2014} & January & 55.40 & 64.16 & 64.01 & 8.61 & \(-\)0.15 & 8466 \\  & February & 52.64 & 66.95 & 57.56 & 4.92 & \(-\)9.39 & 11934 \\ \cline{1-1}  & March & 45.94 & 64.35 & 60.21 & 14.27 & \(-\)4.14 & 80800 \\ \cline{1-1}  & April & 46.04 & 64.36 & 59.13 & 13.09 & \(-\)5.23 & 107137 \\ \hline \multicolumn{2}{c}{Overall mean} & 42.98 & 61.23 & 57.33 & 14.35 & \(-\)3.90 & 815961 \\ \hline \hline \end{tabular}
\end{table}