ACCELERATION OF ENERGETIC PARTICLES BY SHOCK-WAVES FROM LARGE SOLAR-FLARES

The observations in large " solar" proton events are discussed in terms of acceleration of the energetic particles from the ambient solar wind by an interplanetary shock. Many of the large events are found to have a prolonged plateau in their time-intensity profiles. The same value of the intensity, near 100 protons (cm2 sr s MeV)-1, seems to recur in the plateau region in all of these events. These profiles are explained by models of prolonged acceleration by an interplanetary shock. At some distance from the shock, when the particle intensity falls to a value that is sufficiently low, particles stream away from the source with relative ease. The observed profiles are not consistent with models involving particle transport from a single localized point source at the Sun. Element abundance ratios such as Fe/O usually distinguish flare-heated source material (Fe/O ∼ 1) from material accelerated by the interplanetary shock out of the ambient corona or solar wind (Fe/O ∼ 0.1). In several large events that are magnetically well connected to the flare site, Fe-rich material from the flare is observed early in the event, followed by Fe-poor material. Observation of these two-component events requires a well-connected flare, since the Fe-rich material does not have access to field lines far from the flare. The observations argue against any mechanism for cross-field particle transport in the solar corona.