University of Oulu

Väisänen, P., Usoskin, I., & Mursula, K. ( 2019). Long‐term and solar cycle variation of galactic cosmic rays: Evidence for variable heliospheric turbulence. Journal of Geophysical Research: Space Physics, 124, 804– 811.

Long‐term and solar cycle variation of galactic cosmic rays : evidence for variable heliospheric turbulence

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Author: Väisänen, Pauli1; Usoskin, Ilya1,2; Mursula, Kalevi1
Organizations: 1ReSoLVE Centre of Excellence, Space Climate 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, 1.9 MB)
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Language: English
Published: American Geophysical Union, 2019
Publish Date: 2019-04-05


The Sun modulates the flux of galactic cosmic rays (GCR) reaching the Earth’s orbit. GCR flux has been measured by ground‐based neutron monitors (NMs) for several decades, which provides an interesting long‐term monitor of solar activity and the heliospheric magnetic field. Here we study the long‐term evolution of the power spectrum of GCR over the last six solar cycles, using the power law slope in the frequency range 5.56·10⁻⁶ to 2.14·10⁻⁶ Hz (between 50 and 130 hr). We use data from 31 neutron monitors during 1953–2016. We show that the power law slopes vary within the solar cycle, with a Kolmogorov‐type slope observed at solar minimum and a random‐walk‐type slope observed at solar maximum. This implies that the different conditions in the different phases of the solar cycle affect the scaling properties of heliospheric turbulence and, thereby, cosmic ray variability.

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Series: Journal of geophysical research. Space physics
ISSN: 2169-9380
ISSN-E: 2169-9402
ISSN-L: 2169-9380
Volume: 124
Issue: 2
Pages: 804 - 811
DOI: 10.1029/2018JA026135
Type of Publication: A1 Journal article – refereed
Field of Science: 115 Astronomy and space science
Funding: We acknowledge the financial support by the Academy of Finland to the ReSoLVE Centre of Excellence (project 307411). Pauli Väisänen acknowledges the personal research grant from the Finnish Cultural Foundation.
Academy of Finland Grant Number: 307411
Detailed Information: 307411 (Academy of Finland Funding decision)
Copyright information: © 2019. American Geophysical Union. All Rights Reserved.