CLAAS-3: the third edition of the CM SAF cloud data record based on SEVIRI observations

CLAAS-3, the third edition of the Cloud property dAtAset using SEVIRI (Spinning Enhanced Visible
and InfraRed Imager), was released in December 2022. It is based on observations from SEVIRI, on board
geostationary satellites Meteosat-8, 9, 10 and 11, which are operated by the European Organisation for the
Exploitation of Meteorological Satellites (EUMETSAT). CLAAS-3 was produced and released by the EUMETSAT
Satellite Application Facility on Climate Monitoring (CM SAF), which aims to provide high-quality
satellite-based data records suitable for climate monitoring applications. Compared to previous CLAAS releases,
CLAAS-3 is expanded in terms of both temporal extent and cloud properties included, and it is based on partly
updated retrieval algorithms. The available data span the period from 2004 to present, covering Europe; Africa;
the Atlantic Ocean; and parts of South America, the Middle East and the Indian Ocean. They include cloud
fractional coverage, cloud-top height, phase (liquid or ice) and optical and microphysical properties (water path,
optical thickness, effective radius and droplet number concentration), from instantaneous data (every 15 min)
to monthly averages. In this study we present an extensive evaluation of CLAAS-3 cloud properties, based on
independent reference data sets. These include satellite-based retrievals from active and passive sensors, groundbased
observations and in situ measurements from flight campaigns. Overall results show very good agreement,
with small biases attributable to different sensor characteristics, retrieval/sampling approaches and viewing/illumination
conditions. These findings demonstrate the fitness of CLAAS-3 to support the intended applications,
which include evaluation of climate models, cloud characterisation and process studies focusing especially on
the diurnal cycle and cloud filtering for other applications. The CLAAS-3 data record is publicly available via
the CM SAF website at https://doi.org/10.5676/EUM_SAF_CM/CLAAS/V003 (Meirink et al., 2022).