Solar Physics Division Meeting 2000, June 19-22
Session 2. Corona, Solar Wind, Flares, CMEs, Solar-stellar, Instrumentation, Other
Display, Chair: J. Krall, Monday-Thursday, June 19, 2000, 8:00am-6:00pm, Forum Ballroom

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[2.87] Two Classes of Solar Proton Events derived from Onset Time Analysis

S. Krucker, R. P. Lin (SSL, UC Berkeley)

The 3-D Plasma and Energetic Particles experiment on the WIND spacecraft was designed to provide high sensitivity measurements of both suprathermal ions and electrons down to solar wind energies. A statistical survey of 26 solar proton events has been investigated. For all these proton events, a temporally related electron event is observed. The presented results focus on the properties of protons released near the Sun which show a velocity dispersion when detected at 1~AU. The particle flux onset times observed at 1~AU in the energy range between 30keV and 6 MeV suggest that there are two classes of proton events: (1) For one class (70% of the events), the first arriving protons are traveling almost scatterfree as indicated by the derived path lengths between 1.1 and 1.3~AU, (2) whereas the events of the second class show significantly larger path lengths around 2~AU. Relative to the electron release time at the Sun, the almost scatterfree traveling protons of the first class of events are release delayed by 0.5 to 2 hours. For the events of the second class, protons and electrons seemed to be released simultaneously within the accuracy of 20 minutes. Events of the first class are most likely shock accelerated and the late release times suggest an acceleration region at several solar radii away from the Sun. The puzzeling events of the second class could as well be explained by pitch angle scattering or by a succesive later release time at lower energies as by an actual longer path length.

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