Modeling the Shock Aftermath Source of Energetic Particles in the Solar Corona
Leon Kocharov, Marianna Lytova, Rami Vainio, Timo Laitinen, Jarmo Torsti
Recent observations on board the Solar and Heliospheric Observatory (SOHO) indicate that acceleration of solar energetic particles (SEPs) at intermediate scales in the solar corona, between flare acceleration and interplanetary CME-driven shock acceleration, significantly contributes to the production of >10 MeV protons. Coronal shocks seem to be the most plausible candidate for the post-impulsive phase acceleration, which emits \raisebox-0.5ex\textasciitilde1-100 MeV protons into the interplanetary medium for about 1 hr after the flare. We have employed a Monte Carlo technique to model the diffusive shock acceleration of protons in a turbulent layer at the base of the solar wind. We find that a power-law spectrum of energetic protons can be emitted from the trailing turbulent layer left behind the shock into the solar wind for a few tens of minutes after the CME liftoff. In contrast to an earlier expectation, the propagation direction of the shock wave is found not to be crucial. Both outward-propagating and refracting shocks can load the corona with energetic protons. Those protons escape into the interplanetary medium well after the passage of the shock. We have studied successive transformations of the particle spectra during shock acceleration, coronal transport, and possible reacceleration, for different populations of seed particles. The simulated production time profiles and energy spectra are found to be consistent with observations of the 1996 July 9 event by the Energetic and Relativistic Nuclei and Electron (ERNE) instrument on board SOHO. The new model can be easily combined with our previous interplanetary transport models, forming a basis on which to interpret SEP observations made at 1 AU.
ApJ, 620, 1052-1068, 2005