Authors: P. Wurz, R.F. Wimmer-Schweingruber, K. Issautier, P. Bochsler, A.B. Galvin and F.M. Ipavich
Reference: Joint SOHO/ACE workshop, Bern, Switzerland, March 6-9, 2001.
We present a study of the elemental composition of a sub-set of coronal mass ejections, namely events that have been identified of being of the magnetic cloud type (MC). We used plasma data from the SOHO and ACE missions and so far investigated the MCs of 1997 and 1998. The study covers the proton, alpha, and heavy ion abundances. Considerable variations from event to event exist with regard to the density of the individual species with respect to regular "slow" solar wind preceding the MC plasma. However, for the heavy elements, which can be regarded as tracers in the plasma, there is a general trend that the heavier ions are enriched compared to the lighter ions. This trend can be explained by a theoretical model of the precursor plasma loops on the sun before launch of the CME. Proton and alpha particle abundances have to be regarded separately since they represent the main plasma.