Global cloud distribution revealed by combined use of CloudSat/CALIPSO: Comparison using CALIPSO versions 2 and 3 data

We compiled the seasonal variations of the vertical distribution of clouds through a combined analysis of multiyear CloudSat cloud radar and the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) lidar observations between June 2006 and May 2010. The differences between using the previous (version 2, V2) and the latest release (version 3, V3) CALIPSO "Vertical Feature Mask (VFM)" results were also examined. We first developed a cloud mask scheme for CALIPSO and then developed a combined CloudSat/CALIPSO cloud mask based on the ground observations. The VFM (V2) misclassified aerosols and noise signals located in attenuated areas as cloud. Cloud edge detection was also slightly greater by the VFM (V2). In addition, by updating from CALIPSO V2 to V3, the cloud fractions by the VFM dramatically decreased below ∼2.5 km while there is little change in those by the C2. The cloud fraction still differed by as much as 20% between the VFM and our CALIPSO scheme. These results indicate that the issues of CALIPSO VFM (V2) had not been corrected in the latent release VFM (V3) completely. The 4-year averaged seasonal variations were examined by using our combined CloudSat/CALIPSO scheme. In the low-level, cloud coverage is relatively smaller over land and in the Inter Tropical Convergence Zone (ITCZ) depending on season due to a high frequency of cloud overlap. Very large coverage (∼92%) is shown over the western coasts of continents, especially during the summer and fall. The seasonal variation of the ITCZ and the subtropical high in the high-level are observed. A remarkably large cloud coverage of ∼87% exists over the whole area with seasonal variation except for part of the subtropical high region, Greenland and Antarctica.