CLARA-A3¶

CM SAF cLoud, Albedo and surface RAdiation dataset from AVHRR data – Edition 3

Available

At a glance¶

Note on period: The CDR covers 1979-01-01 to 2020-12-31 and the ICDR continues from 2021-01-01 to the present with about 10 days' latency (CM SAF operational products list, 'since 01 Jan 2021'). Some ICDR products, including liquid and ice water path and JCH, end with May 2025.

Overview¶

CLARA-A3 is a global climate data record of clouds, surface albedo and radiation built from more than 40 years of AVHRR imagery on the NOAA and Metop polar orbiters. It provides cloud fraction, cloud-top height, pressure and temperature, phase, optical thickness and liquid and ice water path, together with surface shortwave and longwave fluxes, surface albedo and top-of-atmosphere reflected shortwave and outgoing longwave flux, as daily and monthly means on a 0.25° grid. 1979–2020 is the climate data record (CDR), and from 2021 the record keeps growing as an interim CDR (ICDR) produced the same way.

What changes with the successor¶

CLARA-A2 (A2.1) → CLARA-A3¶

Transition: 2023-04

The third edition, which adds AVHRR/1 data to start the record in 1979 and greatly expands the cloud, albedo and radiation products. A version change within this page.

Sources: Karlsson et al. (2023), ESSD — CLARA-A3 · CM SAF — CLARA-A3 DOI landing page

Available variables¶

Variable names were checked in the CM SAF Product User Manuals (PUM): clouds (SAF/CM/DWD/PUM/CLARA/CLD 3.1, Section 8.3.1), surface albedo (SAF/CM/FMI/PUM/GAC/SAL 3.1, Section 4.1), surface radiation (SAF/CM/DWD/PUM/CLARA/RAD 3.1, Section 4.1) and TOA radiation (SAF/CM/RMIB/PUM/GAC/TOA 1.2, Tables 4-5 to 4-8). Each product comes in its own files (the first three letters of the file name are the product code), and each file also carries observation counts (nobs…), standard deviations and uncertainties. In-file names for IWP and the histogram products (JCH, CWP) could not be confirmed in the PUM text available, so they are left blank.

instantaneous mean accumulated maximum minimum static — instantaneous: value at the time stamp · mean/accumulated/maximum/minimum: over the indicated interval · static: does not change with time

Cloud properties (daily and monthly means, 0.25°)¶

Cloud histograms (monthly)¶

Surface albedo¶

Surface and top-of-atmosphere radiation¶

The full variable list is in the official documentation.

How to get the data¶

• CM SAF Web User Interface (WUI) — Web order (free registration; choose product, period and area → download link by e-mail)
  • The main route, covering every product, per-satellite data and polar grids. Orders stay on the https/sftp servers for 7 days.
• EUMETSAT Data Store — CLARA-A3 CDR and ICDR (EO:EUM:DAT:0874) — Web / Data Store API (eumdac)
  • Holds only a subset of global products from all AVHRRs combined (CFC, CPH, CTO, IWP, LWP, OLR, RSF and SIS daily and monthly means; SAL pentad and monthly means; CTO, CWP and JCH monthly histograms; SDL, SNL, SNS and SRB monthly means). Spatial subsetting is not yet possible. Requires an EUMETSAT account.
• Copernicus CDS — Cloud properties (includes CLARA) — Web / CDS API
  • A copy redistributed by C3S; edition and period may differ from the CM SAF original. Requires an ECMWF account.

Example code¶

Downloads from the Data Store with the API key (consumer key and secret) of an EUMETSAT account. Search parameters differ by collection, so check coll.search_options first. A Data Store 'product' can be a zip archive.

# pip install eumdac
import datetime as dt
import shutil
import eumdac

token = eumdac.AccessToken(("CONSUMER_KEY", "CONSUMER_SECRET"))
store = eumdac.DataStore(token)
coll = store.get_collection("EO:EUM:DAT:0874")   # CLARA-A3 CDR + ICDR
print(coll.title)
print(coll.search_options)                        # available search parameters

products = coll.search(dtstart=dt.datetime(2024, 1, 1), dtend=dt.datetime(2024, 2, 1))
for p in products:
    print(p)
    with p.open() as src, open(src.name, "wb") as dst:
        shutil.copyfileobj(src, dst)
    break                                         # just one, as an example

Practical tips¶

• Since June 2025 the ICDR uses Metop only, so the mix of observation times changed. Split analyses of daily means or diurnal effects at this date.
• The ICDR (2021 onward) uses preliminary ancillary data such as ERA5T and a less accurate visible-channel calibration. From August 2025 its sea-ice input also switched from SSMIS-based OSI-401-d to AMSR2-based OSI-408-a.
• According to the paper, Metop-C was initially left out of the ICDR baseline because of a visible-calibration issue. When using per-satellite Level-2b data, check the file attributes for which satellites are included.
• TOA radiation files (RSF, OLR) produced before March 2026 omit Metop-B and Metop-C from the global attribute 'platforms' (the data values are correct). Watch out if your code selects satellites by that attribute.
• Because the means come from a few polar-orbiter overpasses a day, regions with a strong diurnal cycle (deep convection, marine stratocumulus) can have biased daily means. For diurnal behaviour, look at the geostationary CLAAS-3 (Europe and Africa) or ISCCP as well.

Notices and change history¶

References for your paper¶

Dataset citation¶

CLARA-A3 (CDR and ICDR) — DOI 10.5676/EUM_SAF_CM/CLARA_AVHRR/V003

@misc{clara_a3,
  author    = {Karlsson, Karl-G{\"o}ran and Riihel{\"a}, Aku and Trentmann, J{\"o}rg and Stengel, Martin and Solodovnik, Irina and Meirink, Jan Fokke and Devasthale, Abhay and J{\"a}{\"a}skel{\"a}inen, Emmihenna and Kallio-Myers, Viivi and Eliasson, Salomon and Benas, Nikos and Johansson, Erik and Stein, Diana and Finkensieper, Stephan and H{\aa}kansson, Nina and Akkermans, Tom and Clerbaux, Nicolas and Selbach, Nathalie and Schr{\"o}der, Marc and Hollmann, Rainer},
  title     = {{CLARA-A3}: {CM SAF} cLoud, Albedo and surface RAdiation dataset from {AVHRR} data - Edition 3},
  year      = {2023},
  publisher = {Satellite Application Facility on Climate Monitoring (CM SAF)},
  doi       = {10.5676/EUM_SAF_CM/CLARA_AVHRR/V003}
}

Reference papers¶

CLARA-A3 description paper — DOI 10.5194/essd-15-4901-2023

@article{karlsson2023claraa3,
  author  = {Karlsson, Karl-G{\"o}ran and Stengel, Martin and Meirink, Jan Fokke and Riihel{\"a}, Aku and Trentmann, J{\"o}rg and Akkermans, Tom and Stein, Diana and Devasthale, Abhay and Eliasson, Salomon and Johansson, Erik and H{\aa}kansson, Nina and Solodovnik, Irina and Benas, Nikos and Clerbaux, Nicolas and Selbach, Nathalie and Schr{\"o}der, Marc and Hollmann, Rainer},
  title   = {{CLARA-A3}: The third edition of the {AVHRR}-based {CM SAF} climate data record on clouds, radiation and surface albedo covering the period 1979 to 2023},
  journal = {Earth System Science Data},
  volume  = {15},
  pages   = {4901--4926},
  year    = {2023},
  doi     = {10.5194/essd-15-4901-2023}
}

Acknowledgements¶

CM SAF asks users to show EUMETSAT's copyright and to acknowledge the source with wording such as "The work performed was done (i.a.) by using data from EUMETSAT's Satellite Application Facility on Climate Monitoring (CM SAF).", stating the product edition used (Edition 3, CDR/ICDR).

Information on the datasets used in this study was compiled with the help of the Korean Climate Data Navigator (KCDN) (Sim, 2026; https://doi.org/10.5281/zenodo.23300923).

Links¶

• CM SAF — CLARA-A3 DOI and documentation page (PUM, ATBD, validation reports)
• CM SAF — Operational products (ICDR) list
• CM SAF — File naming convention
• CM SAF — Data records available via the EUMETSAT Data Store (2025-09)
• Karlsson et al. (2023), ESSD