University of Oulu

Gil, A., & Mursula, K. (2018). Comparing two intervals of exceptionally strong solar rotation recurrence of galactic cosmic rays, Journal of Geophysical Research: Space Physics, 123, 6148–6160.

Comparing two intervals of exceptionally strong solar rotation recurrence of galactic cosmic rays

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Author: Gil, A.1,2; Mursula, K.2
Organizations: 1Institute of Mathematics and Physics, Faculty of Scienice, Siedlce University, Siedlce, Poland
2ReSoLVE Centre of Excellence, Space Climate Research Unit, University of Oulu, Oulu, Finland
Format: article
Version: published version
Access: open
Online Access: PDF Full Text (PDF, 5.7 MB)
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Language: English
Published: American Geophysical Union, 2018
Publish Date: 2019-02-28


Two intervals of exceptionally strong recurrence of galactic cosmic ray (GCR) intensity at solar rotation period stand out in recent history, one in 2007–2008 and the other in 2014–2015. We use neutron monitor data from Oulu and Hermanus, solar wind (SW) data, and coronal images to study these intervals. We find that in both cases the source of solar rotation period recurrence was a coronal hole (CH), but CH structures were different. While a large, longitudinally asymmetric CH existed at high southern latitudes in 2014–2015, a low‐latitude CH caused the recurrence in 2007–2008. Spectral properties of GCR and SW parameters reflect these differences. In 2014–2015 the GCR power spectrum density was broad and peaked at a period of 28.9 days, longer than the simultaneous recurrence period of SW speed. In 2007–2008 the GCR power spectrum was narrow and peaked at 27.5 days, exactly the same as for SW speed. The effect of CHs to GCRs was somewhat different in the two cases because of opposite solar polarities in the two intervals. In 2014–2015, during positive polarity when GCRs drift inward from high latitudes, the convection of fast SW from CH reduces the inward GCR drift over a wide range of high heliolatitudes at certain heliolongitudes. In 2007–2008, during negative polarity when GCRs drift inward via the heliospheric current sheet, a low‐latitude CH depletes the GCR flux not only by convection but also by the deflecting heliospheric current sheet away from the ecliptic, whence GCR drift to higher latitudes in a limited longitude range.

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Series: Journal of geophysical research. Space physics
ISSN: 2169-9380
ISSN-E: 2169-9402
ISSN-L: 2169-9380
Volume: 123
Issue: 8
Pages: 6148 - 6160
DOI: 10.1029/2018JA025523
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 272157 founded by the Academy of Finland). A. G. acknowledges The Polish National Science Centre, decision DEC‐2016/22/E/HS5/00406.
Academy of Finland Grant Number: 272157
Detailed Information: 272157 (Academy of Finland Funding decision)
Copyright information: © 2018. American Geophysical Union. All Rights Reserved.