A Comparison of Fe-Rich Solar Energetic Particle Events from Cycle 24 to Those of Cycle 23

Thursday, 18 December 2014
Christina MS Cohen, California Institute of Technology, Pasadena, CA, United States, Richard A Mewaldt, Caltech, Pasadena, CA, United States, Glenn M Mason, JHU / APL, Laurel, MD, United States and Mark E Wiedenbeck, NASA Jet Propulsion Laboratory, Pasadena, CA, United States
Of the first twelve solar energetic particle (SEP) events observed by instruments on the ACE spacecraft during the rising phase of solar cycle 23, nine exhibited Fe/O abundance ratios >2 times the average SEP Fe/O ratio. Several explanations for these ‘Fe-rich’ events were put forth but conclusive testing required simultaneous SEP measurements from distinct longitudinal vantage points. This capability was achieved with the launch of the twin STEREO spacecraft in 2006, however it was not until 2013 that the first significantly Fe-rich SEP event would be measured by both STEREO and ACE. Several additional Fe-rich SEP events have been observed by multiple spacecraft since then. In this presentation we examine the longitudinal dependence of the composition of these events and compare their characteristics to those of the cycle-23 Fe-rich events. We will discuss these results in light of the characteristics of the weaker solar cycle 24 as well as the implications for the proposed scenarios for creating Fe-rich SEP events.