Cosmic ray and solar particle composition measurements in the southern solar polar region

Abstract

This analysis is based on energetic particle measurements covering the energy range 4-20 MeV/n recorded by the COSPIN/LET instrument on the Ulysses spacecraft. Around the end of the year 2000 the Ulysses spacecraft was above the southern polar region at less than 2.5 AU radial distance from the Sun. A preliminary analysis has shown that the abundance ratios He/O and C/O are lower than during the in-ecliptic passage around the last solar maximum and more than ten times higher than during the last southern solar passage. In this work we discuss the abundances measured during three major events at high southern solar latitudes and compare with in-ecliptic and other findings. The elemental abundances of the selected events are consistent with particles having solar energetic particle (SEP) origin. One possible scenario for the production of SEPs is that the particles are accelerated by a CME driven shock, but the most of the corresponding flares of the selected events observed during the southern solar polar region passage occur in the northern solar hemisphere. Furthermore, we found that different periods in the selected time intervals might be characterized by average C/O ratios.