Fe/O variations in large solar energetic particle events

Abstract:

The Fe/O enhancements show significant variations in gradual solar energetic particle (SEP) events. Several possible causes have been suggested including transport effects in the interplanetary space and flare contribution. For 27 gradual SEP events from 2010 to 2014, we examine the relation of the event integrated Fe/O ratios on the event associated flare locations and heliospheric current sheet (HCS) locations. For this study, we use low-energy (∼ 0.5 MeV/n) Fe and O measurements obtained from Suprathermal Ion Telescope (SIT) on Solar Terrestrial Relations Observatories (STEREO) and Ultra Low Energy Isotope Spectrometer (ULEIS) on Advanced Composition Explorer (ACE). We found a moderate anti-correlation between the Fe/O ratios and the absolute longitudinal separation angles from source regions to spacecraft magnetic footpoints. We analyze the Fe/O ratio variations in the same and opposite polarity regions of the associated flares to examine the heliospheric current sheet effect.