Multi-instrument studies of heavy ion solar energetic particle transport

Abstract

In this thesis, an analysis of solar energetic particle (SEP) data from multiple instruments onboard the ACE, SOHO and STEREO spacecraft is presented. The temporal variation and the dependence of heavy ion abundances on solar longitude were studied and quantitatively characterised during SEP events between 2006 and 2016.
Ionic abundances vary over the duration of SEP events, e.g. Fe/O often shows a decrease over time. This behaviour was identified as a common characteristic within the data. The time variation of 36 different ionic pairs was studied for a number of SEP events. The fit constant describing time evolution was found to show ordering by the value of S, given e.g. for Fe/O by SFe/O = (M/Q)Fe/(M/Q)O, where M is the mass number and Q the charge number. The ionic ratios with S>1 decreased over time and those with S<1 showed increases, while ratios with a large S decayed at a higher rate. Anomalous behaviour of ratios involving protons was identified in several events.
The longitudinal dependence of Fe/O simultaneously observed by multiple spacecraft at 1 AU was studied in 12 SEP events. The event-averaged Fe/O values observed by spacecraft at different longitudes varied within a single event, but this variation was less significant than the event-to-event variation. Although the longitudinal dependence was a complicated one, in some events the Fe/O values were higher at a remote observer.
The temporal evolution of heavy ion ratios, which was studied quantitatively for a number of ionic pairs, is consistent with an MQ-dependent interplanetary transport mechanism. The observed longitudinal dependence of event-averaged Fe/O, where higher Fe/O values are observed at a spacecraft that is not well magnetically connected to the source region, cannot be fully explained by the two-class paradigm for classification of SEP events.