# Comparison of SEVIRI-Derived Cloud Occurrence Frequency and Cloud-Top Height with A-Train Data
## 3 Results
### Cloud-Top Height
The cross-section plots are the same types as those in Figure 3, although the figures in the left-hand (right-hand) panel represent the results prior to (following) the BC update. The CPR reflectivity and the CTHs from CALIOP and CPR are the same in both panels, and the SEVIRI CTHs (red crosses) changed as expected. In Figure 6, it is clear that the SEVIRI CTHs became lower owing to the decrease in the CO\({}_{2}\) BC value by 1 K, from 0.85 K to \(-0.15\) K. The heights of low clouds that might be determined by the SL method showed no apparent change, although those for the middle and high clouds, which are generally assigned by the MR method, decreased. The decrease in the mid-level SEVIRI CTHs is remarkable, and it is evident that the BC update led to better results. The problematic mid-level clouds appear to have disappeared after this update. This shows BC change can affect the choice of method between MR and SL in the CTH algorithm. However, the underestimation of CTHs over the deep convective clouds became slightly larger compared to CPR CTHs. Figure 7 shows the scatter plots of CTH from SEVIRI against CPR for each CO\({}_{2}\) channel BC value. The CTH changes with BC values are clear in these plots as well. Prior to the BC change, the distribution of CTHs showed more data points on the lower right-hand side of the one-to-one line in which SEVIRI CTHs showed a slightly large negative bias of \(-0.45\) km (Figure 7a). A large increase  
Figure 5: Time series of the daily validation scores of standard deviation (STD; dotted line), correlation coefficient (solid line), and bias (dashed line) from May 2013 to April 2014. The number of validation data (grey bar) from the cloud-top height (CTH) comparison between the Spinning Enhanced Visible and Infrared Imager (SEVIRI) and Cloud Profiling Radar (CPR) products is also shown. Black x marks on the x-axis indicate the dates the bias correction was updated. in the SEVIRI CTHs is shown in Figure 7b, which resulted in a positive bias of 0.22 km with apparent discontinuity at about 5 km in height. The next two changes resolved these issues, making the SEVIRI CTHs more reliable. The correlation coefficients and the standard deviations did not significantly vary from the BC update. Since the BC increment was updated to \(-0.65\) K in November 2013, SEVIRI has produced more stable values compared to the CPR CTHs, with a correlation coefficient of 0.93, bias of \(-0.27\) km, and standard deviation of 1.61 km. Thus, it is evident that the CO\({}_{2}\) BC increment is critical and needs to be carefully selected in the SEVIRI CTH algorithm. Figure 6: Comparison of Spinning Enhanced Visible and Infrared Imager (SEVIRI) cloud-top heights (CTHs) derived by using different CO\({}_{2}\) bias correction increment (BC) values. The left-panels show the results derived by using the CO\({}_{2}\) BC values prior to the update, and the right-hand panel shows the CTH derived afterward for CPR (Cloud Profiling Radar) overpass 39,413 on 24 September 2013. CTHs from Cloud-Aerosol LiDAR with Orthogonal Polarization (CALIOP), CPR, and SEVIRI are plotted as dark green triangles and white and red crosses, respectively. Figure 7: \(Cont.\)