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Session 74 - The Quiet & Active Sun.
Display session, Friday, January 09
Exhibit Hall,
Gradual solar energetic particle (SEP) events observed at 1 AU are associated with coronal mass ejections (CMEs) that drive shocks which accelerate the ions and electrons to suprathermal energies. However, high energy (> 30 MeV) proton and (> 1 MeV) electron events are nearly always associated with both CMEs and flares, suggesting that the acceleration of those particles, particularly the electrons, could be attributed to the associated flares. Only one clear example of a high energy SEP event without a flare association has been reported previously. We discuss a second such SEP event, on 14 April 1994, associated with a well observed solar X-ray arcade structure spanning \sim 150\deg of solar longitude.
The SEP event, observed by detectors on the IMP-8 and Koronas-I space craft, began about 10 hrs after the beginning of the X-ray event and was temporally and spatially associated with the last of three weak interplanetary type III radio bursts observed by the Ulysses low frequency radio experiment. The delayed onset and rapid rise of the SEP intensities preclude a recent interpretation in which SEPs were accelerated by a shock driven by a CME which erupted at the onset of the X-ray event. Yohkoh soft X-ray subtracted images show a large-scale arcade brightening west of \sim E10\deg beginning about 8 hours after the initial brightening near the east limb. We suggest that the 14 April event consisted of at least two CMEs with progressively westward source regions and that the SEP event was produced in a second shock driven by a later CME.
