University of Oulu

L. Dorman et al 2019 J. Phys.: Conf. Ser. 1181 012070

Investigation of exceptional solar activity in September 2017 : GLE 72 and unusual Forbush decrease in GCR

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Author: Dorman, L.1,2; Tassev, Y.3; Mishev, A.4,5;
Organizations: 1Cosmic Ray Department of IZMIRAN, Moscow, Russia
2Cosmic Ray and Space Weather Center of Tel Aviv University, Israel
3Institute for Space Research and Technology, Bulgarian Academy of Sciences, Bulgaria
4Space Climate Research Unit, University of Oulu, Finland
5Sodankylä Geophysical Observatory, University of Oulu, Finland
6Sofia University "St. Kliment Ohridski", Faculty of Mathematics & Informatics, Bulgaria
Format: article
Version: published version
Access: open
Online Access: PDF Full Text (PDF, 1 MB)
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Language: English
Published: IOP Publishing, 2019
Publish Date: 2019-03-27


The exceptional solar activity in early September 2017 at minimum of solar cycle 24 is analyzed. Intensive solar-terrestrial disturbances was caused by Active Region AR2673, which produced four powerful eruptions class X, including the strongest flare X9.3 of Solar Cycle 24 on September 6, 2017, after which began G4 — Severe geomagnetic storm on 07.–08.09.2017 with Ap = 96, and also the second strongest flare X8.2 of Solar Cycle 24 on September 10, 2017, which generated Ground Level Enhancement (GLE) of cosmic rays. This was GLE72 with increase of solar cosmic ray flux 6% in Oulu Station (Finland) (effective vertical geomagnetic cutoff rigidity: 0.8 GV), and increase 9% in DOMC Antartica and 14% in DOMB Antartica (in the latter case — lead free neutron monitors with effective vertical cutoff rigidity <0.01 GV). The GLE72 develops under the conditions of a deep Forbush decrease (around 15%) in South Pole cusp caused by September 7th Coronal Mass Ejection. The Forbush effect ends on September 11th ( But cosmic ray measurements by flying balloons to the stratosphere over California show that after solar eruptions in September 2017 the radiation levels in stratosphere took more than two months to fully rebound to the conditions of minimal solar activity. This is interesting fact which deserves to be explored in detail. It is precisely the study and interpretation of this process that is concerned with this work.

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Series: Journal of physics. Conference series
ISSN: 1742-6588
ISSN-E: 1742-6596
ISSN-L: 1742-6588
Volume: 1181
Article number: 012070
DOI: 10.1088/1742-6596/1181/1/012070
Host publication: 26th Extended European Cosmic Ray Symposium. 6-10 July 2018, Barnaul, Russia
Conference: Extended European Cosmic Ray Symposium
Type of Publication: A4 Article in conference proceedings
Field of Science: 115 Astronomy and space science
Copyright information: Content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.