Association between interplanetary shock waves and delayed solar particle events

In studying the propagation of energetic charged particles from a large solar flare, we can no longer regard the interplanetary medium as remaining in a steady state: disturbances in the flow of solar wind from these flares may have great effects on the observed fluxes of charged particles. Delayed particle events, also known as ‘energetic storm particle’ events, may exhibit an increase by an order of magnitude or greater in the flux of protons above 10 Mev over a period of the order of 6 hours. These events are seen in association with the passage of an interplanetary shock past the earth. The passage of a ‘corotating region’ and trapping of particle fluxes in the interplanetary blast wave are considered and found to be unable to account for the origin of these events. It is therefore proposed that the particles are accelerated locally at the time of the passage of the interplanetary blast wave.