University of Oulu

Gil, A., Kovaltsov, G.A., Mikhailov, V.V. et al. Sol Phys (2018) 293: 154.

An anisotropic cosmic-ray enhancement event on 07-June-2015 : a possible origin

Saved in:
Author: Gil, Agnieszka1; Kovaltsov, Gennady A.2,3; Mikhailov, Vladimir V.4;
Organizations: 1Institute of Mathematics and Physics, Siedlce University
2Space Climate Research Unit, University of Oulu
3Ioffe Physical-Technical Institute
5Sodankylä Geophysical Observatory, University of Oulu
Format: article
Version: published version
Access: open
Online Access: PDF Full Text (PDF, 2.5 MB)
Persistent link:
Language: English
Published: Springer Nature, 2018
Publish Date: 2018-11-30


A usual event, called anisotropic cosmic-ray enhancement (ACRE), was observed as a small increase (≤5%) in the count rates of polar neutron monitors during 12–9 UT on 07 June 2015. The enhancement was highly anisotropic, as detected only by neutron monitors with asymptotic directions in the southwest quadrant in geocentric solar ecliptic (GSE) coordinates. The estimated rigidity of the corresponding particles is ≤1 GV. No associated detectable increase was found in the space-borne data from the Geostationary Operational Environmental Satellite (GOES), the Energetic and Relativistic Nuclei and Electron (ERNE) on board the Solar and Heliospheric Observatory (SOHO), or the Payload for Antimatter Matter Exploration and Light-nuclei Astrophysics (PAMELA) instruments, whose sensitivity was not sufficient to detect the event. No solar energetic particles were present during that time interval. The heliospheric conditions were slightly disturbed, so that the interplanetary magnetic field strength gradually increased during the event, followed by an increase of the solar wind speed after the event. It is proposed that the event was related to a crossing of the boundary layer between two regions with different heliospheric parameters, with a strong gradient of low-rigidity (<1 GV) particles. It was apparently similar to another cosmic-ray enhancement (e.g., on 22 June 2015) that is thought to have been caused by the local anisotropy of Forbush decreases, with the difference that in our case, the interplanetary disturbance was not observed at Earth, but passed by southward for this event.

see all

Series: Solar physics
ISSN: 0038-0938
ISSN-E: 1573-093X
ISSN-L: 0038-0938
Volume: 293
Issue: 11
Article number: 154
DOI: 10.1007/s11207-018-1375-5
Type of Publication: A1 Journal article – refereed
Field of Science: 115 Astronomy and space science
Funding: The work was partly supported by the projects of the Academy of Finland Centre of Excellence ReSoLVE (No. 272157), CRIPA, and CRIPA-X (No. 304435), and by the Finnish Antarctic Research Program (FINNARP). A.G. acknowledges the Polish National Science Centre, decision number DEC-2016/22/E/HS5/00406. V.M. acknowledges the Ministry of Education and Science of the Russian Federation (contract no. 3.2131.2017).
Academy of Finland Grant Number: 272157
Detailed Information: 272157 (Academy of Finland Funding decision)
304435 (Academy of Finland Funding decision)
Copyright information: © The Author(s) 2018. This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (, which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.