Why is solar cycle 24 an inefficient producer of high-energy particle events?

@article{Vainio2017WhyIS,
  title={Why is solar cycle 24 an inefficient producer of high-energy particle events?},
  author={Rami Vainio and Osku Raukunen and Allan J. Tylka and William F. Dietrich and Alexandr Afanasiev},
  journal={arXiv: Solar and Stellar Astrophysics},
  year={2017}
}
The aim of the study is to investigate the reason for the low productivity of high-energy SEPs in the present solar cycle. We employ scaling laws derived from diffusive shock acceleration theory and simulation studies including proton-generated upstream Alfv\'en 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. Provided… 

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