Correlated Dispersionless Structure in Suprathermal Electrons and Solar Energetic Ions in the Solar Wind

Abstract

Dispersionless modulations in particle intensity are commonly observed in impulsive solar energetic ion events and are occasionally observed within low-energy (less than 1.4 keV) solar electron bursts. The electron burst modulations commonly occur in direct association with discontinuous changes in the intensity of the solar wind electron strahl. Both the energetic ion and the suprathermal electron burst modulations have been interpreted in terms of spatially limited burst source regions and magnetic field-line footpoint motions in the solar atmosphere. Concentrating on impulsive ion modulation events previously reported, we show that there is generally a close connection between the dispersionless modulations in energetic ions in those events and the simultaneous dispersionless modulations in low-energy solar electron bursts and in the electron strahl. This demonstrates that dispersionless modulations in both particle species have a common cause, which we associate with relatively abrupt changes in magnetic connection to the Sun. We find that some of these abrupt connection changes occur at structural boundaries in the solar wind flow. More often, the connection changes appear to arise from field-line footpoint motions or, possibly, solar wind turbulence. To a first approximation, when dispersionless structure is present in both particle species, the electrons and ions appear to be accelerated on the same field lines in spatially confined regions in the corona. Overall, however, the data suggest that electron burst source regions usually are more spatially uniform, have considerably broader spatial extents than the ion sources, or both.