Solar Energetic Particles

Populations of energetic ions and electrons are major constituents of the heliospheric plasma environment. They are ubiquitous, extending from sites in the lower corona to the interface of the heliosphere with the interstellar medium. The energies of these particles extend from solar wind energies up to ~10 GeV for ions and ~100 MeV for electrons. A solar energetic particle (SEP) event (one case in Figure 5) occurs when particles (protons and heavy ions) emitted by the Sun become accelerated either close to the Sun during a flare or in the interplanetary space by shocks driven by CMEs. The UNH/CME group carries out research on SEPs majorly through observations, simulations, and analytical analysis. For observations, the group studies the characteristics and evolution of SEPs associated with CMEs and other solar transients in the (inner) heliosphere by the instruments from multiple spacecraft, e.g., spacecraft at Lagarangian-1 point (e.g., GOES, WIND, ACE), STEREO, and the recently launched Parker Solar Probe (PSP) and Solar Orbiter (SolO). PSP and SolO provide unique detections of SEPs much closer to the Sun, and colleagues at UNH took apart in the development of the particle detectors at PSP and SolO (check the Space Science Center experimental research group). For simulations, the group has used a 3D plasma hybrid model (Figure 6), which is currently under development at UNH, to model shocks and turbulence in the interplanetary medium, and model the associated ions as particles (kinetically) and electrons as a fluid. The group also uses analytical tools to interpret data from SEP events and study the transport and acceleration of SEPs.

Proton intensity observed during a Solar Energetic Particle event.


Figure 5. Proton intensity observed by GOES13 during the SEP event on 10 September 2017.

3D hybrid simulations of solar energetic particles.

Figure 6. The results in the 3D hybrid simulations. Left: density (n) and velocity convergence (-∇∙V) associated with different shock-normal angles (θBn). Right: time series of peculiar energy spectrogram (ε), density and velocity convergence. From Young et al. (2020).