University of Oulu

Väisänen, P., Usoskin, I., Kähkönen, R., Koldobskiy, S., & Mursula, K. (2023). Revised reconstruction of the heliospheric modulation potential for 1964–2022. Journal of Geophysical Research: Space Physics, 128, e2023JA031352.

Revised reconstruction of the heliospheric modulation potential for 1964–2022

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Author: Väisänen, Pauli1; Usoskin, Ilya1,2; Kähkönen, Riikka1;
Organizations: 1Space Physics and Astronomy Research Unit, University of Oulu, Oulu, Finland
2Sodankylä Geophysical Observatory, University of Oulu, Oulu, Finland
Format: article
Version: published version
Access: open
Online Access: PDF Full Text (PDF, 3.7 MB)
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Language: English
Published: American Geophysical Union, 2023
Publish Date: 2023-05-11


Galactic cosmic rays (GCRs) impinge on the Earth’s atmosphere and generate showers of secondary particles in nuclear collisions with the atmospheric constituents. The flux of GCR near Earth is subjected to heliospheric modulation driven by solar magnetic activity and to geomagnetic shielding. Variability of the GCR flux is continuously monitored by the worldwide network of ground-based neutron monitors (NMs) since the 1950s. Solar modulation is often quantified via the force-field approximation parameterized by the modulation potential ϕ, which can be evaluated from the global NM data set. Here we revisit the methodology and provide an updated and extended reconstruction of the heliospheric modulation potential for 1964–2022, using a recent NM yield function and the measurements of the 10 most stable high-latitude NMs. A key improvement in the reconstructed heliospheric modulation potential is the new daily resolution, which provides new opportunities for further research. Reconstruction uses the root-mean square error (RMSE) minimization to find the optimum daily and monthly scaling factors for individual NMs. The stability of the reconstruction is analyzed and the errors are estimated. The mean level of uncertainty is low, generally within ±1%, but it is found to depict marginal variability at the 11-year, annual and 27-day timescales at the <1% level, indicating that a very small systematic uncertainty is still present.

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Series: Journal of geophysical research. Space physics
ISSN: 2169-9380
ISSN-E: 2169-9402
ISSN-L: 2169-9380
Volume: 128
Issue: 4
Article number: e2023JA031352
DOI: 10.1029/2023JA031352
Type of Publication: A1 Journal article – refereed
Field of Science: 115 Astronomy and space science
Funding: This work was also partly supported by the Academy of Finland (projects ESPERA, Grant 321882, and QUASARE, Grant 330064), and University of Oulu (Project SARPEDON).
Academy of Finland Grant Number: 321882
Detailed Information: 321882 (Academy of Finland Funding decision)
330064 (Academy of Finland Funding decision)
Dataset Reference: The obtained reconstructions are tabulated in the Supporting Information S1 and published freely through -repository (citation: Väisänen et al. (2023)) with CC4 BY-NC license and data physically stored in University of Oulu's Cosmic ray station servers. Data will also be made available in, with updates available in the future.
Copyright information: © 2023. The Authors. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.