WIND Observations of Energetic Solar Proton Events Down to keV Energies

Sa"m Krucker

Abstract

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 52 solar proton events has been investigated. For all 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 analysis of the spectral, temporal, and spatial observations reveal the following main results: 1) Dispersive protons show a low energy cut off between 0.1 and 1 MeV.2) There are two classes of proton events: 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, whereas the events of the second class show significantly larger path lengths  around 2 AU.3) 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.

      Authors: Sa"m Krucker, Robert P. Lin

  Organization: Space Sciences Laboratory
     Telephone: 510 643 3101
           Fax: 510 643 8302
        e-mail: krucker@ssl.berkeley.edu
       Address: University of California, Berkeley
   Berkeley, CA 94720-7450