CLARA-A2.1: CM SAF cLoud, Albedo and surface RAdiation dataset from AVHRR data - Edition 2.1

The CLARA-A2.1 record provides cloud properties, surface albedo and surface radiation parameters derived from the AVHRR sensor onboard polar orbiting NOAA and METOP satellites. It includes and temporally extends the second version of the record (Karlsson et al., 2016; CLARA-A2 DOI:10.5676/EUM_SAF_CM/CLARA_AVHRR/V002) now providing data from 1982/01 to 2019/06, i.e., for 37.5 years. Original visible radiances were inter-calibrated and homogenised, using MODIS data as a reference, before applying the various parameter retrievals. The inter-calibration was based on an original method introduced by Heidinger et al. (2010) which was updated (MODIS Collection 6) and extended. CLARA-A2.1 features a range of cloud products: cloud mask, cloud top temperature/pressure/height, cloud thermodynamic phase, and (for liquid and ice clouds separately) cloud optical thickness, particle effective radius and cloud water path. Cloud products are available as monthly and daily averages and also as daily resampled global products (Level 2b) for individual satellites. Cloud parameter results are also presented as multi-parameter distributions (i.e., joint frequency histograms of cloud optical thickness, cloud top pressure and cloud phase) for daytime conditions. Surface albedo is presented as monthly and pentad (5 day) averages of the broadband black-sky albedo and is derived using all available data during the studied period. Surface radiation products are provided as monthly averages for the downwelling shortwave (including also daily averages) and the down- and upwelling longwave components. The monthly and daily averages are available on a 0.25°x0.25° global grid. Surface albedo and cloud products are also provided in two equal area grids with a resolution of 25 km x 25 km covering the polar regions. Daily resampled cloud products (level 2b) are provided in a global grid with a resolution of 0.05°x0.05°. For the latter, also a probabilistic cloud mask is added as an experimental product. A summary of the CLARA-A2.1 characteristics and a comprehensive evaluation of the data are available through a comprehensive set of documentations documents including user guides and, algorithm descriptions.