Surface Radiation and Albedo

Solar surface radiation data of high quality is essential for the appropriate monitoring and analysis of the Earth's radiation budget and the climate system. Further, they are crucial for the efficient planning and operation of solar energy systems. However, well maintained surface measurements are rare in many regions of the world and over the oceans. There, satellite derived information is the exclusive observational source. This emphasizes the important role of satellite based surface radiation data.

Figure 1: Climatology of global radiation (SIS) based on SARAH-2.1 (left), SARAH-E (middle) and CLARA-A2 (right)

The CM SAF provides various surface radiation parameters in the long-wave and shortwave spectral ranges, as well as the surface albedo. The main surface radiation fluxes are provided by the CLARA and the SARAH product families, which provide a global and regional coverage, respectively. The global CLARA data record is based on polar orbiting satellites, while the SARAH data record is based on geostationary METEOSAT satellites that mainly cover Europe, Africa, the Atlantic and parts of South America (SARAH family). Data from the IODC (Indian Ocean Data Coverage) Service is also used to provide the SARAH-E data records that cover the Indian Ocean, Indian and parts of China. SARAH-E has been generated by a collaboration of the CM SAF and the European Commission’s Joint Research Center and is also available via the CM SAF Web User Interface. The climatology of global radiation of all three product families is shown in Figure 1.

Any climate data record (CDR) (CLARA, SARAH, SARAH-E) provides the ‘surface incoming solar radiation’ (SIS), also called ‘global radiation’ or ‘surface irradiance’. The SARAH data record further provides the direct radiation (SID) and direct normal radiation (DNI), which is of special interest for renewable energy applications. The effective cloud albedo (CAL) is provided, too. The sunshine duration (SDU) and spectrally resolved irradiance (SRI) is exclusively available by the SARAH-2 data record. The CLARA data record additionally provides the surface downward and upward longwave radiation, SDL and SOL, respectively.

Furthermore, the CLARA climate data record provides the ‘surface albedo’ (SAL), which specifically means the broadband directional-hemispherical reflectance (black-sky albedo) of the Earth’s surface. The data is provided for all land, ocean, and snow/ice surfaces globally at 5-day and monthly mean temporal resolution.

The spatial resolutions range from 0.25 x 0.25 degree (for CLARA) to 0.05 x 0.05 degree (for SARAH). For certain CLARA parameters including SAL, 25 x 25 km equal-area projection subsets covering the Polar Regions are available. The temporal resolutions range from monthly (all data records) over daily to 30-minutes instantaneous data (only SARAH-2). As it is standard for each CM SAF product, the data products are documented and validated in detail; specific documents are available on the website.

Figure 2: Time series of relative anomalies [%] of summer (June, July, August) sunshine duration for Germany based on the combination of TCDR an ICDR (SARAH-2.1 and ICDR SEVIRI Radiation), covering 1983-2018.

Consistent with the climate data records of SARAH-2.1 and CLARA-A2.1 so-called ‘Interim Climate Data Records’ (ICDR) provide regularly updated ‘near-real time’ data on surface radiation parameters after the end of the temporal coverage of the climate data records. This enables climate monitoring applications by extending the CDR with the ICDR with 5 day timeliness. An example of the analysis of the sunshine duration based on SARAH-2 CDR and ICDR SEVIRI Radiation is shown in Figure 2.

All CM SAF CDRs and in particular the Surface Radiation Products are DOI-referenced and widely used by different user communities including climate analysis, climate modelling and renewable energies. More information on the data and its potential applications can be found in the following references.

All CM SAF data products are freely available via the CM SAF Web User Interface.

References:
DOIs of the latest CDR products:
10.5676/EUM_SAF_CM/CLARA_AVHRR/V002_01
10.5676/EUM_SAF_CM/SARAH/V002_01
10.5676/DWD/JECD/SARAH_E/V001_01_01

Direct link to the ICDR data:
https://wui.cmsaf.eu/safira/action/viewICDRDetails?acronym=SARAH_V002_ICDR
https://wui.cmsaf.eu/safira/action/viewICDRDetails?acronym=CLARA_AVHRR_V002_ICDR

Selected Journal Articles:

• Huld T., Müller R., Gambardella A. (2012): A new solar radiation database for estimating PV performance in Europe and Africa, Solar Energy, 86 (1803-1815), doi: 10.1016/j.solener.2012.03.006.
• Karlsson K., Anttila K., Trentmann J., Stengel M., Fokke Meirink J., Devasthale A., Hanschmann T., Kothe S., Jääskeläinen E., Sedlar J., Benas N., van Zadelhoff G., Schlundt C., Stein D., Finkensieper S., Håkansson N., Hollmann R. (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.
• Müller R., Pfeifroth U., Träger-Chatterjee C., Trentmann J., Cremer R. (2015): Digging the METEOSAT Treasure—3 Decades of Solar Surface Radiation, Remote Sensing, 7 (8067-8101), doi: 10.3390/rs70608067.
• Pfeifroth U., Sanchez-Lorenzo A., Manara V., Trentmann J., Hollmann R., 2018: Trends and Variability of Surface Solar Radiation in Europe Based On Surface- and Satellite-Based Data Records, Journal of Geophysical Research: Atmospheres, 123 (1735–1754), doi: 10.1002/2017JD027418.
• Riihelä, A., Manninen, T., Laine, V., Andersson, K., and Kaspar, F. (2013): CLARA-SAL: a global 28 yr timeseries of Earth's black-sky surface albedo, Atmos. Chem. Phys., 13 (3743-3762), doi: 10.5194/acp-13-3743-2013.
• Schwarz M., Folini D., Hakuba M., Wild M. (2017): Spatial Representativeness of Surface-Measured Variations of Downward Solar Radiation, Journal of Geophysical Research: Atmospheres, 122 (13319-13337), doi: 10.1002/2017JD027261.
• Urraca R., Gracia-Amillo A., Huld T., Martinez-de-Pison F., Trentmann J., Lindfors A., Riihelä A., Sanz-Garcia A. (2017): Quality control of global solar radiation data with satellite-based products, Solar Energy, 158 (49-62), doi: 10.1016/j.solener.2017.09.032.

JT / April2021