This data set is only available for a restricted user group, please contact us if you want to access these data.
RESTRICTED only accessible in CEN/MPI net or via CliSAP login What does that mean?
CLARA-A2 stands for "CM SAF cLouds, Albedo RAdiation data record, AVHRR-based, Edition 2" and comprises a suite of radiation and cloud parameters derived within the EUMETSAT Climate Monitoring Satellite Application Facility (CM-SAF) from Advanced Very High Resolution Radiometer (AVHRR) data.
Surface incoming shortwave radiation is computed following Müller et al. (2009, see references). Cloud detection & masking is carried out with the AVHRR-PPS package (see Dybbroe et al., 2005 under references of the CLARA-A2 albedo product). Additionally required independent surface albedo and aerosol information is based on climatologies (GADS/OPAC and SARB/CERES), other meteorological information is taken from ERA-Interim reanalysis data. For cloudy grid cells look-up tables are used. The temporal averaging takes into account the diurnal cycle of solar radiation.
The surface outgoing longwave radiation is basically based on respective ERA-Interim data corrected for differences in terrain elevation and spatial resolution.
The surface downwelling longwave radiation is basically as well based on respective ERA-Interim data corrected for terrain elevation and cloud cover effects.
We offer edition 2 of the CLARA data set, i.e. CLARA-A2, only for internal use.
The data set was included into the ICDC data base on May 24 2018.
|Surface downwelling shortwave radiation (SIS)||W/m²||Also available with daily temporal resolution|
|as above but with low accuracy||W/m²||not compliant with CM-SAF target accuracy (e.g. for polar regions)|
|Surface downwelling shortwave radiation standard deviation||W/m²|
|Number of surface downwelling shortwave radiation observations per grid cell||--|
|Number of daily averages used for the monthly average value of SIS||--|
|Clear sky surface downwelling shortwave radiation (SISCLS)||W/m²||Model result|
|Number of daily averages used for the monthly average value of SISCLS||--|
|Surface downwelling longwave radiation (SDL)||W/m²|
|Surface downwelling longwave radiation standard deviation||W/m²|
|Number of surface downwelling longwave radiation observations per grid cell||--|
|Surface outgoing longwave radiation (SOL)||W/m²|
Period and temporal resolution:
- 1982-01 to 2015-12
Coverage and spatial resolution:
- Spatial resolution: 0.25 degrees x 0.25 degrees, equally spaced lat/lon grid (Climate Modeling Grid, CMG)
- Geographic longitude:-179.875°E to 179.875°E
- Geographic latitude: -89.875°N to 89.875°N
- Dimension: 1440 columns x 720 rows
- Altitude: --
The data set does not include separate uncertainty estimates.
It does contain, however, information about the standard deviation per grid cell which could be taken as a measure of uncertainty. It contains also information about the number N of valid radiation values per grid cell and the number of days with valid values used to compute the monthly averages. Generally, for a daily average at least 20 observations per grid cell are required. Monthly averages are only derived when at least 20 valid daily averages are available for the respective grid cell.
Evaluation of the product confirms that the target accuracy of 10 W/m² is met for the two surface incoming / downwelling radiation products; for the surface outgoing longwave radiation the target accuracy is not met (14 W/m² is the actual accuracy).
The (often low) total number of satellite overpasses - particularly during the years before 1992 - and hence very low number of overlapping swaths causes many gaps in the surface incoming shortwave radiation product. Because of limited accuracy also over snow-covered areas often no data of the surface incoming shortwave radiation is provided. It can therefore not be recommended to derive large-scale averages from the CLARA-A2 record of this parameter.
Both longwave products depend largely on ERA-Interim atmospheric re-analysis data and are hence not suited for model evaluation.
ICDC / CEN / University of Hamburg
email: stefan.kern (at) uni-hamburg.de
- Algorithm Theoretical Basis Document (ATBD)
- Product User Manual (PUM)
- Validation Report
- Karlsson, K.-G., et al., 2017, CLARA-A2: the second edition of the CM SAF cloud and radiation data record from 34 years of global AVHRR data, Atmospheric Chemistry and Physics, 17, 5809-5828, doi:10.5194/acp-17-5809-2017.
- Karlsson, K.-G., et al. 2015, Advancing the uncertainty characterisation of cloud masking in passive satellite imagery: Probabilistic formulations for NOAA AVHRR data, Remote Sens. Environ., 158, 126–139, doi:10.1016/j.rse.2014.10.028.
- Karlsson, K.-G., et al., 2013, CLARA-A1: a cloud, albedo, and radiation dataset from 28 yr of global AVHRR data, Atmospheric Chemistry and Physics, 13, 5351-5367, doi:10.5194/acp-13-5351-2013.
- Heidinger, A.K., et al., 2010, Deriving an inter-sensor consistent calibration for the AVHRR solar reflectance data record, International Journal of Remote Sensing, 31, 6493-6517.
- Hess, M., et al., 1998, Optical properties of aerosol and clouds: The software package OPAC, Bulletin of the American Meteorological Society, 79(5), 831-844.
- Mueller, R., et al., (2009), The CM-SAF operational scheme for the satellite based retrieval of solar surface irradiance - A LUT based eigenvector hybrid approach, Remote Sensing of Environment, 113, 1012-1024, doi://10.1016/j.rse.2009.01.012.
The citation for this data set is:
Karlsson, Karl-Göran; Anttila, Kati; Trentmann, Jörg; Stengel, Martin; Meirink, Jan Fokke; Devasthale, Abhay; Hanschmann, Timo; Kothe, Steffen; Jääskeläinen, Emmihenna; Sedlar, Joseph; Benas, Nikos; van Zadelhoff, Gerd-Jan; Schlundt, Cornelia; Stein, Diana; Finkensieper, Stephan; Håkansson, Nina; Hollmann, Rainer; Fuchs, Petra; Werscheck, Martin (2017): CLARA-A2: CM SAF cLoud, Albedo and surface RAdiation dataset from AVHRR data - Edition 2, Satellite Application Facility on Climate Monitoring, DOI:10.5676/EUM_SAF_CM/CLARA_AVHRR/V002, https://doi.org/10.5676/EUM_SAF_CM/CLARA_AVHRR/V002.
All intellectual property rights of the CM SAF products belong to EUMETSAT. The use of these products is granted to every interested user, free of charge. If you wish to use these products, EUMETSAT copyright credit must be shown by displaying the words "copyright (year) EUMETSAT" on each of the products used.