A1 Refereed original research article in a scientific journal
Annual integral solar proton fluences for 1984-2019
Authors: Raukunen Osku, Usoskin Ilya, Koldobskiy Sergey, Kovaltsov Gennady, Vainio Rami
Publisher: EDP SCIENCES S A
Publication year: 2022
Journal: Astronomy and Astrophysics
Journal name in source: ASTRONOMY & ASTROPHYSICS
Journal acronym: ASTRON ASTROPHYS
Article number: A65
Volume: 665
First page : 1
Last page: 14
Number of pages: 14
ISSN: 0004-6361
eISSN: 1432-0746
DOI: https://doi.org/10.1051/0004-6361/202243736
Web address : https://doi.org/10.1051/0004-6361/202243736
Self-archived copy’s web address: https://research.utu.fi/converis/portal/detail/Publication/176753792
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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