Active-region footpoints (top, red) yield enhanced SEP Fe/O; coronal-hole footpoints (bottom, blue) lead to low SEP Fe/O.   NRL researchers have traced the SEP compositional variability back to the nature of the solar region that provides seed particles for shock acceleration.
Active-region footpoints (top, red) yield enhanced SEP Fe/O; coronal-hole footpoints (bottom, blue) lead to low SEP Fe/O. NRL researchers have traced the SEP compositional variability back to the nature of the solar region that provides seed particles for shock acceleration.

Objective
To identify sources and to quantify the characteristics of various coronal seed populations that give rise to large solar energetic particle (SEP) events produced by coronal mass ejection (CME)-driven shocks.
At high energies, relevant to spacecraft design and operation, large SEP events are highly variable in their size, duration, spectral shape, and ionic composition. These variable factors determine the nature of the radiation hazard posed to space-based systems. This project focuses on discovering the contribution of seed-particle populations to this variability, as an input for future SEP predictive capability for satellite operations.

Approach

  • Identify CME/flare sources and analyze SEP characteristics of large events from Solar Cycles 23 & 24
  • Identify footpoint of the Sun-Earth magnetic field line; characterize its properties
  • Investigate connections between footpoint characteristics and variable SEP properties
  • Implement inferred seed particle distributions into SEP acceleration and transport codes
  • Combine SEP (HPC) acceleration code with shock parameters from CME propagation code
  • Apply NRL solar flare gamma ray and neutron production codes to quantify coronal suprathermal seed protons from neutron decay

Deliverable/Value/Accomplishment

  • Understanding of how remotely-observed solar quantities (such as photospheric magnetic fields) govern the suprathermal seed population that gives rise to SEPs.
  • Ability to identify ‘all clear’ periods when SEP radiation hazard is minimal.
  • Large database of well-characterized SEP events for improvement of empirical probabilistic models (like CREME96) used by space-system designers
  • Transition to operations: warnings to operators on the duration and severity of SEP events