University of Oulu

Imprints of long-term solar variability on cosmic rays and terrestrial archives

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Author: Asvestari, Eleanna1
Organizations: 1University of Oulu, Faculty of Science, Physics
Format: ebook
Version: published version
Access: open
Online Access: PDF Full Text (PDF, 2.5 MB)
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Language: English
Published: Oulu : University of Oulu, 2016
Publish Date: 2021-04-09
Thesis type: Doctoral Dissertation
Defence Note: Academic Dissertation to be presented with the assent of the Doctoral Trainning Committee of Technology and Natural Sciences of the University of Oulu for public discussion in the Auditorium IT116, Linnanmaa, on 2nd December, 2016, at 12 o’clock.
Tutor: Professor Ilya Usoskin
Professor Kalevi Mursula
Reviewer: Professor Valery M. Ostryakov
Doctor Margaret A. Shea
Opponent: Professor Katya Georgieva
Kustos: Professor Ilya Usoskin


Galactic cosmic rays (GCRs) arriving at Earth, interact with nuclei of atmospheric gases leading to the production of cosmogenic radionuclides. The latter, following a series of processes, are eventually stored in terrestrial archives such as ice cores and tree rings. The information that can be collected, traces back millions of years. Since the solar activity has a large impact on GCRs, via modulation processes in the heliosphere, one can gain knowledge about the solar activity in the past using the cosmogenic radionuclide records. The primary goal of our study is to reconstruct the solar activity in the past combining all the available information from different cosmogenic radionuclides and databases obtained from different locations on Earth. The principle idea is that, using terrestrial archives and existing models of radionuclide production, the GCR flux can be reconstructed over the past millennia. Thereafter, the solar activity, after applying a model correlating the GCR flux to different solar parameters, can be reconstructed. To achieve this it was necessary to develop an empirical model reconstructing the tilt angle of the Heliospheric Current Sheet (HCS), one of the important heliospheric factors influencing cosmic ray propagation inside the heliosphere. The HCS tilt has been traced with observations since 1976. Following, a semi-empirical model of GCR modulation in the heliosphere was developed using measurements and reconstructions of the heliospheric parameters that play a major role in the modulation processes. In particular these are the open solar magnetic flux, the solar magnetic polarity and the HCS tilt angle. With this model the cosmic ray variability on Earth in millennial time scales was reconstructed and used as an input parameter in existing models, calculating the production and deposition of the cosmogenic radionuclides ¹⁴C and ¹⁰Be. The results were then compared with the data aiming to achieve the best fit that will lead to best reconstruction of the solar activity.

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Osajulkaisut / Original papers

Osajulkaisut eivät sisälly väitöskirjan elektroniseen versioon / Original papers are not included in the electronic version of the dissertation.

  1. Usoskin, I. G., Arlt, R., Asvestari, E., Hawkins, E., Käpylä, M., Kovaltsov, G. A., Krivova, N., Lockwood, M., Mursula, K., O’Reilly, J., Owens, M., Scott, C. J., Sokoloff, D. D., Solanki, S. K., Soon, W., & Vaquero, J. M. (2015). The Maunder minimum (1645–1715) was indeed a grand minimum: A reassessment of multiple datasets. Astronomy & Astrophysics, 581, A95.

  2. Asvestari, E., & Usoskin, I. G. (2016). An empirical model of heliospheric cosmic ray modulation on long-term time scale. Journal of Space Weather and Space Climate, 6, A15.

  3. Asvestari, E., Usoskin, I. G., Kovaltsov, G. A., Owens, M. J., & Krivova, N. (2016). Test of different sunspot number series against the cosmogenic isotope records. Manuscript submitted for publication.

  4. Asvestari, E., Willamo, T., Gil, A., Usoskin, I. G., Kovaltsov, G. A., Mikhailov, V. V., & Mayorov, A. (in press). Analysis of Ground Level Enhancements (GLE): Extreme solar energetic particle events have hard spectra. Advances in Space Research.

    Rinnakkaistallennettu versio / Self-archived version

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Series: Report series in physical sciences
ISSN: 1239-4327
ISSN-L: 1239-4327
ISBN: 978-952-62-1465-8
ISBN Print: 978-952-62-1464-1
Issue: 108
Type of Publication: G5 Doctoral dissertation (articles)
Field of Science: 115 Astronomy and space science
Copyright information: © University of Oulu, 2016. This publication is copyrighted. You may download, display and print it for your own personal use. Commercial use is prohibited.