A1 Refereed original research article in a scientific journal
Why is solar cycle 24 an inefficient producer of high-energy particle events?
Authors: Vainio R, Raukunen O, Tylka AJ, Dietrich WF, Afanasiev A
Publisher: EDP SCIENCES S A
Publishing place: LES ULIS CEDEX A
Publication year: 2017
Journal: Astronomy and Astrophysics
Journal name in source: ASTRONOMY & ASTROPHYSICS
Journal acronym: ASTRON ASTROPHYS
Article number: ARTN A47
Volume: 604
Number of pages: 9
ISSN: 1432-0746
eISSN: 1432-0746
DOI: https://doi.org/10.1051/0004-6361/201730547
Web address : 10.1051/0004-6361/201730547
Abstract
Aims. The aim of the study is to investigate the reason for the low productivity of high-energy SEPs in the present solar cycle.Methods. We employ scaling laws derived from diffusive shock acceleration theory and simulation studies including proton-generated upstream Alfven waves to find out how the changes observed in the long-term average properties of the erupting and ambient coronal and/or solar wind plasma would affect the ability of shocks to accelerate particles to the highest energies.Results. Provided that self-generated turbulence dominates particle transport around coronal shocks, it is found that the most crucial factors controlling the diffusive shock acceleration process are the number density of seed particles and the plasma density of the ambient medium. Assuming that suprathermal populations provide a fraction of the particles injected to shock acceleration in the corona, we show that the lack of most energetic particle events as well as the lack of low charge-to-mass ratio ion species in the present cycle can be understood as a result of the reduction of average coronal plasma and suprathermal densities in the present cycle over the previous one.
Aims. The aim of the study is to investigate the reason for the low productivity of high-energy SEPs in the present solar cycle.Methods. We employ scaling laws derived from diffusive shock acceleration theory and simulation studies including proton-generated upstream Alfven waves to find out how the changes observed in the long-term average properties of the erupting and ambient coronal and/or solar wind plasma would affect the ability of shocks to accelerate particles to the highest energies.Results. Provided that self-generated turbulence dominates particle transport around coronal shocks, it is found that the most crucial factors controlling the diffusive shock acceleration process are the number density of seed particles and the plasma density of the ambient medium. Assuming that suprathermal populations provide a fraction of the particles injected to shock acceleration in the corona, we show that the lack of most energetic particle events as well as the lack of low charge-to-mass ratio ion species in the present cycle can be understood as a result of the reduction of average coronal plasma and suprathermal densities in the present cycle over the previous one.
UTU Research Portal