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Article

On the Assessment of Hourly Means of Solar Irradiance at Ground Level in Clear-Sky Conditions by the ERA5, JRA-3Q, and MERRA-2 Reanalyses

by
Yves-Marie Saint-Drenan
* and
Lucien Wald
MINES Paris, PSL University, Centre Observation Impacts Energie (O.I.E.), 06904 Sophia-Antipolis, France
*
Author to whom correspondence should be addressed.
Atmosphere 2025, 16(8), 949; https://doi.org/10.3390/atmos16080949 (registering DOI)
Submission received: 24 June 2025 / Revised: 11 July 2025 / Accepted: 14 July 2025 / Published: 7 August 2025
(This article belongs to the Section Atmospheric Techniques, Instruments, and Modeling)

Abstract

Meteorological reanalyses are one of the means to assess the solar irradiance reaching the ground. This paper deals with estimates of the hourly means of irradiance in clear-sky conditions provided by the ERA5, JRA-3Q, and MERRA-2 reanalyses. They are compared to coincident ground-based measurements from 28 BSRN stations located worldwide, selected by a new algorithm for detecting cloud-free instants. Although ERA5 most often underestimates measurements, it is quite reliable over time because it captures the temporal variability of measurements well and provides a constant level of uncertainty. JRA-3Q offers a complex pattern with negative and positive biases depending on station and season. It captures well the temporal variability but, as a whole, is not reliable over time. None of the three reanalyses is reliable in space. Because of its use of the mean solar time instead of the true solar time, MERRA-2 suffers many drawbacks over intraday scales. Its statistical indicators exhibit marked patterns depending on the season and station. Its assimilation of aerosol properties offers advantages when compared to the climatologies used in ERA5 and JRA-3Q. This work exposes the strengths and weaknesses of each reanalysis in clear-sky conditions and formulates suggestions to providers for further improvements.
Keywords: solar radiation; clear-sky; meteorological reanalysis; BSRN; aerosol; detection of clear-sky instants solar radiation; clear-sky; meteorological reanalysis; BSRN; aerosol; detection of clear-sky instants

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MDPI and ACS Style

Saint-Drenan, Y.-M.; Wald, L. On the Assessment of Hourly Means of Solar Irradiance at Ground Level in Clear-Sky Conditions by the ERA5, JRA-3Q, and MERRA-2 Reanalyses. Atmosphere 2025, 16, 949. https://doi.org/10.3390/atmos16080949

AMA Style

Saint-Drenan Y-M, Wald L. On the Assessment of Hourly Means of Solar Irradiance at Ground Level in Clear-Sky Conditions by the ERA5, JRA-3Q, and MERRA-2 Reanalyses. Atmosphere. 2025; 16(8):949. https://doi.org/10.3390/atmos16080949

Chicago/Turabian Style

Saint-Drenan, Yves-Marie, and Lucien Wald. 2025. "On the Assessment of Hourly Means of Solar Irradiance at Ground Level in Clear-Sky Conditions by the ERA5, JRA-3Q, and MERRA-2 Reanalyses" Atmosphere 16, no. 8: 949. https://doi.org/10.3390/atmos16080949

APA Style

Saint-Drenan, Y.-M., & Wald, L. (2025). On the Assessment of Hourly Means of Solar Irradiance at Ground Level in Clear-Sky Conditions by the ERA5, JRA-3Q, and MERRA-2 Reanalyses. Atmosphere, 16(8), 949. https://doi.org/10.3390/atmos16080949

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