Particle acceleration and transport from the Sun to the outer heliosphere
Time dependence of heavy ion ratios in SEP events
Peter Zelina
Silvia Dalla (University of Central Lancashire)
University of Central Lancashire
Eruptive events such as solar flares and coronal mass ejections can accelerate ions and electrons into the heliosphere, causing solar energetic particle (SEP) events. Time resolved in situ measurements show that heavy ion ratios, e.g. Fe/O, are not constant but exhibit temporal evolution over the duration of an SEP event. In the case of Fe/O, the ratio is observed to decrease by as much as 2 orders of magnitude, but other ratios may show less temporal variation or even increase over time. What causes the ratio abundances to change over time? Is there a parameter that is ordering the observed behaviour? In this work, we systematically characterise the decreases (increases) of heavy ion ratios in several SEP events. We consider several pairings of elements and automatically determine the decay/increase time constant B describing their ratio's evolution. We find that B scales with the ratio of M/Q values of the two elements. In some SEP events, we find that time dependences of X/H, where X stands for an abundant SEP element, do not follow the same trend as ratios with respect to other ions. We discuss possible causes of the time dependence of elemental ratios within the context of our observational results.
13:30 - 15:00
EX - C3 (150)