Variations of high time resolution heavy ion characteristics in the complex May 2005 ICME

Coronal Mass Ejections~(CMEs) are extremely dynamical large scale events in which plasma-not only the coronal plasma-is ejected into the interplanetary space. Their interplanetary counterparts measured in-situ are Interplanetary Coronal Mass Ejections (ICMEs), which is also an important part of space weather.

Even though the kinetic properties of the plasma might change because of dynamic effects occurring during the expansion of the CME, the heavy ion characteristics remain unchanged after it leaves the low corona. Charge states of heavy ions reflect important information about the coronal temperature profile due to the freeze-in effect, while elemental abundances indicate potential source regions of the plasma.

With the help of the Pulse Height Analysis (PHA) data from the Solar Wind Ion Composition Spectromet (SWICS) on board the Advanced Composition Explorer (ACE), combined with a newly developed multi-population model, we are able to conduct a high time resolution (12 minutes) case study on a complex ejecta detected by ACE in May 2005. This case lasted more than 80 hours and caused a strong geomagnetic response, with a Dst index at -247.

Multiple discontinuous periods with highly charged heavy ions are identified, elemental abundances also differ during those ”hot” periods. Heavy ion characteristics provide us an unique opportunity to see the boundaries of different parts of an ICME.