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JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 101, NO. A12, PAGES 27,521–27,532, 1996

Particle flows observed in ejecta during solar event onsets and their implication for the magnetic field topology

I. G. Richardson

Department of Astronomy, University of Maryland, College Park


H. V. Cane

Laboratory for High Energy Astrophysics, NASA Goddard Space Flight Center, Greenbelt, Maryland


Abstract

We investigate the magnetic field topology of ejecta (the interplanetary manifestations of solar mass ejections) by using observations of energetic particle anisotropies made by the Goddard Space Flight Center instruments on the ISEE 3, Helios 1, and Helios 2 spacecraft at ≤1 AU from the Sun. In particular, we investigate particle flows observed following the onsets of 39 solar energetic particle events which occurred when the observing spacecraft was located in a preexisting ejecta. To infer when the spacecraft was located in an ejecta, we examine a wide range of indicators of the presence of ejecta including magnetic cloud signatures, bidirectional energetic ion flows, bidirectional solar wind electron heat fluxes, and depressed proton plasma temperatures. We find that inside ejecta, the particle arrival direction in the ecliptic plane varies widely from event to event, with at least 30% of the events showing flows from the east of the Sun. In contrast, in 60 similar events observed outside ejecta, the particle arrival directions are consistent with flows from the Sun along near-Parker spiral field lines in >90% of cases. We also discuss multiple-spacecraft observations of three particle events which illustrate the contrasting particle flows observed during the same event by spacecraft in different solar wind structures. We conclude that the observations are consistent with the presence of nonspiral magnetic fields, including looped magnetic field lines connected to the Sun, in at least a subset of ejecta.

Received 4 June 1996; accepted 27 August 1996.

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Citation: Richardson, I. G., and H. V. Cane (1996), Particle flows observed in ejecta during solar event onsets and their implication for the magnetic field topology, J. Geophys. Res., 101(A12), 27,521–27,532.