Concurrent solar and corotating interaction region particle events in August 1996

The energetic particle telescope ERNE onboard SOHO registered a continuous particle flux enhancement during August 7-18, 1996. The particle event was limited in the low energy range from 1.6 to 8 MeV during the first week of the event. It originated from a corotating interaction region (CIR). At 163 0 UT on August 13, an additional new flux of energetic particles emerged wi th maximum energies above 50 MeV. The southwest directed coronal mass eject ion (CME) is the most probable source of the high energy particles. Our spe ctral analysis revealed a two-component structure with a hard Bessel-type s pectrum (alpha T similar to 0.02) of the CME-injected particles and a soft power law spectrum (index s similar to 4.0) of CIR particles from 1630 UT t ill 1000 UT on August 14. In the following 3 hours the intensities above 3 MeV decreased more than 10-fold. During the plateau-type intensity maximum phase the intensities remained almost isotropic in the wide ERNE/HED view c one. We claim that the reason for the drop was that the direct connection t o the CME was lost but the connection to the CIR was still maintained. The flux of >12 MeV protons still prevailing in interplanetary space had probab ly been injected earlier by the CME-associated event in its very early phas e in the solar atmosphere, and trapped there between the CIR and the Sun. T he spectrum of these protons was of power form and very hard, s similar to 1.9. During August 15, the high-energy part hardened further, s similar to 1.1. At the same time, the intensities increased, leading to a second inten sity maximum during the first half of August 16. Finally, on August 18, a d isconnection from the CIR took place in all energy channels.