University of Oulu

Raukunen, O., Usoskin, I., Koldobskiy, S., Kovaltsov, G., & Vainio, R. (2022). Annual integral solar proton fluences for 1984–2019. Astronomy & Astrophysics, 665, A65.

Annual integral solar proton fluences for 1984–2019

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Author: Raukunen, O.1,2; Usoskin, Ilya3; Koldobskiy, Sergey3;
Organizations: 1Space Research Laboratory, University of Turku, Turku, Finland
2Aboa Space Research Oy, Turku, Finland
3Space Physics and Astronomy Research Unit and Sodankylä Geophysical Observatory, University of Oulu, Oulu, Finland
Format: article
Version: published version
Access: open
Online Access: PDF Full Text (PDF, 2.7 MB)
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Language: English
Published: EDP Sciences, 2022
Publish Date: 2022-09-15


Aims: Long-term fluxes or integral fluences of solar energetic particles (SEPs), and their variability within and beyond the 11-year solar cycle, make an important contribution to space physics. However, large uncertainties exist in the evaluation of average SEP fluxes or fluences over the last few decades, as they have been assessed by different methods and from different datasets. Here we revisit the derivation of annual integral SEP fluences from available data based on in situ measurements since 1984.

Methods: We reconstructed a full time series of integral SEP fluxes above 10, 30, 60, 100, and 200 MeV for the period from 1984 to 2019 using observations performed by the GOES satellites. Intercalibration of the fluxes was performed via a linear relation between overlapping pairs of observations in order to obtain a uniform dataset. Galactic cosmic ray (GCR) background subtraction and identification of SEP event periods were carefully performed, allowing for a precise calculation of annual SEP fluences.

Results: Annual integral fluences of SEPs with energies above 10, 30, 60, 100, and 200 MeV were calculated for the period from 1984 to 2019 (solar cycles 22–24), along with their uncertainties. It is shown that solar cycle 24 was significantly (by a factor of 5–8) weaker in the SEP fluence than the preceding cycles 22 and 23. The cumulative occurrence probability of years with the fluence above a given value is found to be perfectly described by the Weibull distribution. This can be used as a projection for the occurrence of solar extreme eruptive events on the secular timescales.

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Series: Astronomy and astrophysics
ISSN: 0004-6361
ISSN-E: 1432-0746
ISSN-L: 0004-6361
Volume: 665
Article number: A65
DOI: 10.1051/0004-6361/202243736
Type of Publication: A1 Journal article – refereed
Field of Science: 115 Astronomy and space science
Copyright information: © O. Raukunen et al. 2022. Open Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License (, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. This article is published in open access under the Subscribe-to-Open model. Subscribe to A&A to support open access publication.