Low‐energy particle response to CMEs during the Ulysses solar maximum northern polar passage

Abstract

Near the end of 2001, the Ulysses spacecraft transited the northern polar regions of the heliosphere, above heliographic latitudes of 71°N. During this period (September–November 2001), Ulysses remained immersed in polar coronal hole solar wind flow and observed five intense solar energetic particle events and five interplanetary coronal mass ejections. We study the effects that the passage of these ejecta produced on the low‐energy (77 keV to 20 MeV) ion and near‐relativistic (38–315 keV) electron populations. Whereas observations at the heliocentric distance of ∼1 AU and in the ecliptic plane usually show low‐energy ion intensity depressions associated with the passage of fast ejecta, observations for the five ejecta at high heliographic latitudes and in high‐speed solar wind streams showed increases in the low‐energy ion intensities. The observation of energetic particle intensity enhancements at the entry of Ulysses into these five ejecta was due to (1) the lack of an intense shock‐accelerated population propagating outside the ejecta, (2) the efficient confinement of low‐energy ions within the ejecta, and (3) the effects that local magnetic structures have on particle transport. At 1 AU and in the ecliptic plane, low‐energy ion intensities usually peak at the arrival of shocks and the highest intensities are observed outside the coronal mass ejections. At high heliographic latitudes and in high‐speed solar wind streams, however, the shocks were not efficient accelerators of energetic particles, and consequently the highest intensities were observed inside the coronal mass ejections. We discuss the possible origins of the energetic particles observed inside the ejecta, the possible mechanisms for confining these particles within the ejecta, and the effects that magnetic field structures had on modulating the energetic particle intensities observed by Ulysses.