a Three-Dimensional View of Major Solar Energetic Particle Events

Using SOHO particle and EUV detection and radio spectrograms from both ground-based and spaceborne instruments, we study the first phase of two major solar energetic particle (SEP) events associated with solar eruptions centered at different solar longitudes. A major solar energetic particle (SEP) event observed on 4 April 2000 was associated with western solar flare and fast and wide coronal mass ejection (CME). The SEP event near the eruption's center starts with deka-MeV/n helium- and relativistic electron- rich production from coronal sources identified with the electromagnetic diagnostics. Observations of the initial phase of the "well-connected" major SEP event support the idea that acceleration of SEPs starts in the helium-rich plasma of the eruption's core well behind the CME leading edge, in association with coronal shocks and/or magnetic reconnection caused by the CME liftoff; and those "coronal" components dominate during the first ~1.5 hour of the SEP event, not yet being hidden by the CME-bow shock in solar wind. The 12 September 2000 eruption's center was angle-distant with respect to the SOHO-connected heliolongitude. The event began with a first-phase, hard-spectrum SEP production that was extremely poor in helium, and onset of the first stage of the SEP event as observed on SOHO was delayed by an extra half hour, compared to the "well-connected" event of 4 April 2000. At magnetic connection to the eruption's periphery, onset of SEP emission is delayed for a time of the lateral expansion that is visualized by global coronal (EIT) waves. In both cases, the initial, coronal phase of SEP event is followed by the second-phase SEP production associated with a decelerating CME-driven shock wave in solar wind, which accelerates deka-MeV/n ions from a helium-poor particle population for ~6--12 hours, until the interplanetary shock slows down to below 1000 km/s. Based on these and other SOHO observations, we discuss what findings we can expect from STEREO in the SOHO era perspective.