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We fit the $sim$0.1-500 MeV/nucleon H-Fe spectra in 46 large SEP events surveyed by Desai et al. (2016) with the double power-law Band function to obtain a normalization constant, low- and high-energy parameters $gamma_a$ and $gamma_b$; and break energy $E_B$. We also calculate the low-energy power-law spectral slope $gamma_1$. We find that: 1) $gamma_a$, $gamma_1$, and $gamma_b$ are species-independent within a given SEP event, and the spectra steepen with increasing energy; 2) $E_B$s are well ordered by Q/M ratio, and decrease systematically with decreasing Q/M, scaling as (Q/M)$^alpha$ with $alpha$ varying between $sim$0.2-3; 3) $alpha$ is well correlated with Fe/O at $sim$0.16-0.23 MeV/nucleon and CME speed; 4) In most events: $alpha<$1.4, the spectra steepen significantly at higher energy with $gamma_b$-$gamma_a >$3; and 5) Seven out of 9 extreme SEP events (associated with faster CMEs and GLEs) are Fe-rich, have $alpha >$1.4, have flatter spectra at low and high energies with $gamma_b$-$gamma_a <$3. The species-independence of $gamma_a$, $gamma_1$, and $gamma_b$ and the systematic Q/M dependence of $E_B$ within an event, as well as the range of values for $alpha$ suggest that the formation of double power-laws in SEP events occurs primarily due to diffusive acceleration at near-Sun CME shocks and not due to scattering in the interplanetary turbulence. In most events, the Q/M-dependence of $E_B$ is consistent with the equal diffusion coefficient condition while the event-to-event variations in $alpha$ are probably driven by differences in the near-shock wave intensity spectra, which are flatter than the Kolmogorov turbulence spectrum but still weaker compared to that inferred for the extreme events.
An interval of exceptional solar activity was registered in early September 2017, late in the decay phase of solar cycle 24, involving the complex Active Region 12673 as it rotated across the western hemisphere with respect to Earth. A large number o
Heavy ion ratio abundances in Solar Energetic Particle (SEP) events, e.g.~Fe/O, often exhibit decreases over time. Using particle instruments on the ACE, SOHO and STEREO spacecraft, we analysed heavy ion data from 4 SEP events taking place between De
Solar Energetic Particles (SEPs) possess a high destructive potential as they pose multiple radiation hazards on Earth and onboard spacecrafts. The present work continues a series started with the paper by Borovikov et al.(2018) describing a computat
The PAMELA satellite experiment is providing first direct measurements of Solar Energetic Particles (SEPs) with energies from about 80 MeV to several GeV in near-Earth space, bridging the low energy data by other space-based instruments and the Groun
Data from the PAMELA satellite experiment were used to measure the geomagnetic cutoff for high-energy ($gtrsim$ 80 MeV) protons during the solar particle events on 2006 December 13 and 14. The variations of the cutoff latitude as a function of rigidi