Dispersionless modulations in low-energy solar electron bursts and discontinuous changes in the solar wind electron strahl

The solar wind experiment on the Advanced Composition Explorer ( ACE) has detected at least 328 impulsive solar electron bursts that exhibited energy and angle dispersion at onset at energies below 1.4 keV in the interval from 1 January 1998 through 30 September 2003. Discontinuous, dispersionless modulations in burst intensity and pitch angle occurred in a subset of these events. These dispersionless modulations were similar to discontinuous modulations in the solar wind electron strahl intensity often observed at these same energies at other times. During the bursts themselves, dispersionless modulations in burst intensity commonly, but not always, were associated with discontinuous changes in the underlying strahl intensity. At times the burst intensity modulations were correlated with the strahl modulations and at times they were anticorrelated with the strahl modulations. We find that the variety of types of dispersionless burst/strahl modulations observed within low-energy solar electron bursts can largely be explained in terms of a simple model that assumes spatially limited burst source regions, a strahl intensity that varies with coronal magnetic connection point, and magnetic field line foot point motions in the solar atmosphere during the 2-4 days it takes solar wind plasma and the embedded heliospheric magnetic field to travel from the Sun to 1 AU.