# Comparison of SEVIRI-Derived Cloud Occurrence Frequency and Cloud-Top Height with A-Train Data  
[PERSON]  
1 National Meteorological Satellite Center, Korea Meteorological Administration, 64-18 Guam-gil, Gwanghyewon-myeon, Jincheon-gun, Chuncheonbuk-do 27803, Korea 1  
[PERSON]  
2 Met Office, FitzRoy road, Exeter, Devon EX1 3 PB, UK; [EMAIL_ADDRESS] (P.N.F. ); [EMAIL_ADDRESS] (R.W.S.) 2  
[PERSON]  
2 Met Office, FitzRoy road, Exeter, Devon EX1 3 PB, UK; [EMAIL_ADDRESS] (P.N.F. ); [EMAIL_ADDRESS] (R.W.S.) 2  
and [PERSON]  
3 Department of Atmosphere Sciences, Yonsei University, 50 Yonsei-ro, Seodaemun-gu, Seoul 03722, Korea; [EMAIL_ADDRESS] 3  
Correspondence: [EMAIL_ADDRESS]; Tel. : +82-70-7850-5903  
regional and global scales. Satellites can provide information on the global distribution of cloud cover and cloud properties and variations. Measurements from passive satellite imagers at visible to thermal infrared wavelengths on board many geostationary and polar orbiting satellites provide a wealth of information on cloud properties. The current operational geostationary satellite in Europe, Meteosat Second Generation (MSG) has the 12-channel Spinning Enhanced Visible and Infrared Imager (SEVIRI) and provides high temporal frequency observations every 15 min to help deliver information on cloud characteristics. The UK Met Office uses data from Meteosat satellites for weather analysis and forecasting. Cloud parameters are derived operationally from radiances observed by SEVIRI and include cloud detection, cloud-top temperature, height, and effective cloud amount (ECA), which is the product of the fractional coverage and the cloud emissivity. These parameters are used as image interpretation tools for forecasters and as inputs to numerical weather prediction (NWP) and automated nowcasting systems [4]. Validation of these satellite-derived cloud parameters is important for understanding their accuracies and characteristics for use in various applications. Many validation studies have been conducted with ground-based reference data, such as observations from cloud radar [5], Cloudnet [6], and aircraft experiments [7]. However, these validations are obviously restricted in space and time. Moreover, inter-satellite comparisons of cloud parameters are more resistant to the deficiencies in temporal and spatial coverage and have thus been effective in determining the value and limitations of various satellite products. The Cloud Retrieval Evaluation Workshop (CREW) has led research activities in evaluating the strengths and weaknesses of the well-established algorithms that retrieve cloud properties from passive imager instruments such as SEVIRI, Advanced Very-High-Resolution radiometer (AVHRR), and Moderate Resolution Imaging Spectroradiometer (MODIS) on board both polar and geostationary satellites. CREW working group members operate the highly-advanced cloud retrieval algorithms. The UK Met Office has participated in CREW and has provided cloud products including the CREW Common Database for five \"golden\" days, which have been inter-compared and validated against observations from the A-Train satellite constellation by Cloud-Aerosol LiDAR and Infrared Pathfinder Satellite Observations (CALIPSO), CloudSat, and Aqua. The A-Train Validation of Aerosol and Cloud Properties from SEVIRI (AVAC-S) software [8] was developed in the European Organisation for the Exploitation of Meteorological Satellites (EUMETSAT) to support this activity. In this study, AVAC-S software was developed and used for validating the UK Met Office cloud products for one year of data. This study is organized as follows. Section 2 briefly introduces the cloud data from SEVIRI, Cloud Profiling Radar (CPR), and Cloud-Aerosol LiDAR with Orthogonal Polarization (CALIOP), which are used in this comparison study. In addition, the AVAC-S system and the methodology used to validate cloud products are presented. In Section 3, some details of SEVIRI cloud cover and cloud-top height (CTH) validation results are compared with CPR and CALIOP products.