Energetic Particle Characteristics in the High-Latitude Heliosphere near Solar Maximum

Abstract

This review is focused on the energetic particle observations made from the Ulysses spacecraft during the period it spent at high latitudes above the streamer belt in 1999/2000. The relativistic electron intensity has exhibited a significant number of impulsive increases, which are attributed to solar flares, up to latitudes of S80° degrees. These events were normally accompanied by increases in ions of energies above a few MeV nucleon⁻¹. However, there are significant differences in the case with which ions and electrons are transported in latitude, which is interpreted as a velocity effect. In general the MeV ion increases persist at the same peak intensity level up to November 2000, the latest data we have analysed. This is in contrast to the relativistic electrons, where the peak intensity of the events increases above ~S50°, with the largest event occurring above S79^°. The discrete events at Ulysses are compared with those in the ecliptic (from ACE). We note that unlike the first high latitude passage of Ulysses in 1994, approaching solar minimum, where the solar wind was consistently above 750 km s⁻¹ after S40°, in the 2000 passage, significant deviations from the in-ecliptic solar wind pattern have not yet (S80^°) been realised. Implications of this on the energetic particle characteristics are discussed.