Abstract
Abstract. The present work deals with two well-known databases of hourly mean of solar irradiance that are derived from satellite imagery: the CAMS Radiation Service version 3.2, abbreviated as CAMS-Rad and part of the Copernicus Atmosphere Monitoring Service version 3.2 (CAMS), and the HelioClim-3 version 5, abbreviated as HC3v5. It adds up to the continuous documentation of these two databases that demonstrates that both databases capture the temporal and spatial variability of the solar radiation and are reliable sources of data. The spatial consistency of the uncertainties of these databases is verified against measurements performed within a dense network of ground stations in the Netherlands from the Royal Meteorological Institute KNMI for the period 2014–2017. For the CAMS-Rad database, the correlation coefficients between ground measurements and estimates are around 0.94–0.97 for irradiance E and 0.85–0.89 for clearness index KT. The bias ranges between −12 and 27 W m−2 (−4 % and 10 %). The standard deviation for E is almost constant at all stations and around 67 W m−2 (24 %) except at Valkenburg (57 W m−2, 20 %) and De Bilt (73 W m−2, 27 %). For this database, the statistical indicators are constant at inland stations showing the spatial consistency of the performances of CAMS-Rad dataset. At seashore stations, statistical indicators are more variable. The sea proximity influences CAMS-Rad performances and a weak spatial consistency is observed near seashore. For the HC3v5 database, the correlation coefficients are around 0.96–0.98 for E and 0.86–0.91 for KT. The bias ranges between −3 and 15 W m−2 (−1 % and 5 %). The standard deviation ranges between 48 (17 %) and 60 W m−2 (22 %). It is constant at inland stations and around 54 W m−2 (20 %) with peaks at Ell (59 W m−2, 21 %) and De Bilt (60 W m−2, 22 %). For this database, statistical indicators are constant at all stations as a whole, showing a strong spatial consistency of uncertainties. An exception is the standard deviation which tends to decrease at the seashore stations and is close to 50 W m−2 (17 %); this could be related to the general trend of decreasing standard deviation with increasing KT already reported in the scientific literature. As a whole, it is found that both databases are reliable sources on solar radiation in the Netherlands.
Highlights
The downwelling solar radiation received at ground level is known to be an essential variable in many domains (Lefèvre et al, 2014), including weather and climate, and life on Earth for animals, plants (Bois et al, 2008; Colombo et al, 2009; Wagner et al, 2012) and humans (Juzeniene et al, 2011), or solar energy
The coefficients are slightly less for KT; they range between 0.85 and 0.89 for Copernicus Atmosphere Monitoring Service (CAMS)-Rad and between 0.86 and 0.91 for HC3v5
This denotes a clear influence of the proximity to the coast or of the latitude on the bias. No such influence is found for the standard deviation
Summary
The downwelling solar radiation received at ground level is known to be an essential variable in many domains (Lefèvre et al, 2014), including weather and climate, and life on Earth for animals, plants (Bois et al, 2008; Colombo et al, 2009; Wagner et al, 2012) and humans (Juzeniene et al, 2011), or solar energy. Several meteorological reanalyses provide estimates of E for the entire world and span several decades back in time, such as ERA-Interim, ERA5, MERRA, and MERRA-2 Published validations of these reanalyses against measurements of E performed by instruments based inland or offshore found that the bias is not constant in space and reported that these reanalysis exhibits large standard deviation of errors (Bengulescu et al, 2017; Boilley and Wald, 2015; Jones et al, 2017; Trolliet et al, 2018). Several databases have been created from the Meteosat images Two of these are dealt with in this article: the CAMS Radiation Service, abbreviated as CAMS-Rad and part of the Copernicus Atmosphere Monitoring Service (CAMS), and the HelioClim-3 version 5, abbreviated as HC3v5. Time series used for this work are freely available on request These databases are routinely validated against ground-based measurements.
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