An anisotropic cosmic-ray enhancement event on 07-June-2015 : a possible origin
|Author:||Gil, Agnieszka1; Kovaltsov, Gennady A.2,3; Mikhailov, Vladimir V.4;|
1Institute of Mathematics and Physics, Siedlce University
2Space Climate Research Unit, University of Oulu
3Ioffe Physical-Technical Institute
5Sodankylä Geophysical Observatory, University of Oulu
|Online Access:||PDF Full Text (PDF, 2.5 MB)|
|Persistent link:|| http://urn.fi/urn:nbn:fi-fe2018113049561
|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.
|Type of Publication:||
A1 Journal article – refereed
|Field of Science:||
115 Astronomy and space science
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 (Academy of Finland Funding decision)
304435 (Academy of Finland Funding decision)
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