Nazov: Time dependence of heavy ion ratios in solar events

Prednasajuci: Peter Zelina

Abstrakt: 

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.