# Comparison of SEVIRI-Derived Cloud Occurrence Frequency and Cloud-Top Height with A-Train Data
## 3 Results
### Cloud Occurrence Frequency

Table 4: Probability of detection (POD), false alarm ratio (FAR), proportion correct (PC), and Kuiper’s skill score (KSS) scores of Spinning Enhanced Visible and Infrared Imager (SEVIRI) cloud detection compared with Cloud Profiling Radar (CPR) and Cloud-Aerosol LiDAR with Orthogonal Polarization (CALIOP) with regard to surface type. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Surface Type**} & \multicolumn{3}{c}{**Mean Cloud Coverage (\%)**} & \multicolumn{2}{c}{**SEVIRI Bias (\%)**} & \multirow{2}{*}{**Number of Data**} \\ \cline{2-2} \cline{6-7}  & **CPR** & **CALIOP** & **SEVIRI** & **CPR** & **CALIOP** & \\ \hline All & 42.98 & 61.23 & 57.33 & 14.35 & \(-\)3.90 & 815961 \\ Land & 35.67 & 56.87 & 44.74 & 9.07 & \(-\)12.14 & 291108 \\ Ocean & 47.03 & 63.65 & 64.32 & 17.28 & 0.67 & 524853 \\ \hline \hline \end{tabular} Note: CPR: Cloud Profiling Radar; CALIOP: Cloud-Aerosol LiDAR with Orthogonal Polarization.  
\end{table} 
Table 3: Mean cloud occurrence frequencies and the biases of Spinning Enhanced Visible and Infrared Imager (SEVIRI) cloud products with regard to the surface type (land/ocean) for a one-year validation period. that the CPR COFs were distributed less with much lower frequency than those of SEVIRI except for the desert areas that are nearly cloudless over the year, such as Sahara and Kalahari in Africa, and Syria and Arabia in the Middle East. In contrast with the CPR data, the CALIOP estimation of COFs was significantly higher and showed relatively high frequency. This trend was particularly apparent over the tropical convective areas of South America, Africa, and the Atlantic Ocean near the equator. The COF of SEVIRI was relatively higher in the mid- and high-latitude regions, where the satellite zenith angle of Meteosat-10 became larger. Except for some desert regions, positive values appear to dominate the COF difference map between SEVIRI and CPR over all areas, particularly showing larger positive bias on the South Atlantic Ocean, most oceans of the Northern Hemisphere, and over Eastern Europe, which indicates that CPR detected fewer clouds than SEVIRI. The difference in the COF between SEVIRI and CALIOP was smaller. CALIOP captured higher frequency in the tropical region. In contrast, SEVIRI detected a slightly higher amount of clouds than CALIOP in mid- and high-latitude regions. In order to investigate the seasonal COF changes, COF distributions for a boreal summer month (July 2013) and a boreal winter month (December 2013) are shown in Figure 2. We selected the December data because of the lack of data for January and February. For these maps, all possible observations were used from 11 to 31 July and from 1 to 31 December. In July, the cloud belt of the ITCZ was located near 0\({}^{\circ}\)-10\({}^{\circ}\)N, and the cloud-free zones were distributed broadly within the  
Figure 1: Cloud occurrence frequency maps for Cloud Profiling Radar (CPR), Cloud-Aerosol LiDAR with Orthogonal Polarization (CALIOP), and Spinning Enhanced Visible and Infrared Imager (SEVIRI; upper panels) and the difference maps of SEVIRI compared with CPR and CALIOP products (lower panels) for a one year comparison period between May 2013 and April 2014. The brightness and the colours represent averaged values over a 2\({}^{\circ}\) latitude \(\times\) 2\({}^{\circ}\) longitude grid box. north and south boundaries of the ITCZ related to the subtropical ridges. Very low COF regions are shown through the Sahara Desert, the Mediterranean, and the Middle East, and over southern Africa including Kalahari. Moreover, high COF zones occurred over the Eastern Atlantic over the Sub-Tropical High. This COF pattern was more noticeable in SEVIRI data than those of CPR and CALIOP. In December, the ITCZ moved to the south, and the contrast of cloudy and clear zones were weakened. The COFs increased over southern Africa and South America, where they were very low in summer.