EGU25-10807, updated on 15 Mar 2025
https://doi.org/10.5194/egusphere-egu25-10807
EGU General Assembly 2025
© Author(s) 2025. This work is distributed under
the Creative Commons Attribution 4.0 License.
Assessment of CAMS Radiation Service over France in different sky conditions
Diego Rodrigues de Miranda1, Faiza Azam1, Jorge Lezaca1, Yves-Marie Saint-Drenan2, and Marion Schroedter-Homscheidt1
Diego Rodrigues de Miranda et al.
  • 1DLR (German Aerospace Center) - Institute of Networked Energy Systems, Energy Systems Analysis, Oldenburg, Germany (diego.rodriguesdemiranda@dlr.de)
  • 2MINES Paris, Université PSL Centre Observation Impacts Energie (O.I.E.), Sophia-Antipolis, France

The assessment of solar irradiance variability is relevant for evaluating irradiance-based models, resource assessment and forecasting applications in the solar energy field. One well-established irradiance-based model database for solar project development is the Copernicus Atmosphere Monitoring Service (CAMS) through its CAMS Radiation Service (CRS) that offers historical all-sky solar irradiance estimates. In this work, the accuracy of the CRS GHI product over France is evaluated under different irradiance variability conditions by applying a sky condition classification method based on 1-minute Global Horizontal Irradiance (GHI) observations. A dense network of GHI measurements over France with more than 230 ground stations in the year 2015 is used as a case study.

The classification method is based on a visual interpretation of GHI measurement patterns for the Baseline Surface Radiation Network (BSRN) station of Carpentras during the years 2012 and 2013, which forms a reference database. This reference database is composed of 280 manually classified hours in minute resolution for GHI into eight different classes (from clear sky to variable and overcast sky conditions). Ten variability indices (VIs) are applied in the classification scheme including the clear sky index (kc); the average, maximum and standard deviation of the absolute values for the first derivative of kc; the VIs proposed by Stein et al. (2012) and Coimbra et al. (2013); VIs based on envelopes curves obtained according to the local maxima and minima time-series; and three VIs that counts GHI values overpassing the clear sky irradiance in 3%, 5% and 10%. The classification model consists of three main steps: a discrimination filter, a probability classification approach and a median distance-based approach. The discrimination filter is a counting step that checks if the VIs are inside the Carpentras reference database domain for a particular class. The class with the most VIs will be the selected class. If the maximum number of VIs counted is the same for two or more classes, then a probability classification approach makes the class decision. This probability approach uses Kernel density estimation to calculate the neighborhood probability of a specific VI to be part of one of the eight classes. The class with the higher mean probability over all classes will be selected. Finally, for all the cases outside the domain of the reference database, the median distance-based approach with normalized VIs is applied as presented by Schroedter-Homscheidt et al. (2018). 

The evaluation of the CRS GHI over France is shown in Figure 1. The highest values of the Root Mean Square Deviation (RMSD) are found in class 6, which is mostly dominated by broken clouds. Also classes 4, 7 and 8 present large RMSD. The identification of this broken cloud conditions cluster is useful for further developments of the CRS algorithm in these challenging situations. 

 

 

 

Figure 1 – CRS RMSD in different sky conditions over France (hourly resolution).

How to cite: Rodrigues de Miranda, D., Azam, F., Lezaca, J., Saint-Drenan, Y.-M., and Schroedter-Homscheidt, M.: Assessment of CAMS Radiation Service over France in different sky conditions, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10807, https://doi.org/10.5194/egusphere-egu25-10807, 2025.