Authors: P. Wurz , R.F. Wimmer-Schweingruber , K. Issautier , P. Bochsler , A. B. Galvin , J. A. Paquette and F. M. Ipavich
Reference: American Institute Physics on Solar Wind X, in print, 2002.
We present a study of the elemental composition of a sub-set of coronal mass ejections, namely events which have been identified of being of the magnetic cloud type (MC). We used plasma data from the MTOF sensor of the CELIAS instrument of the SOHO mission. So far we have investigated MCs of 1997 and 1998. The study covers the proton, alpha, and heavy ion elemental 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, two general features are observed. First, for the heavy elements (carbon through iron), which can be regarded as tracers in the solar wind plasma, a mass-dependent enrichment of ions monotonically increasing with mass is observed. The enrichment can be explained by a previously published theoretical model assuming coronal plasma loops on the solar surface being the precursor structure of the MC. Second, when comparing the MC plasma to regular solar wind composition, a net depletion of the lighter ions, helium through oxygen, is always observed. Proton and alpha particle abundances have to be regarded separately since they represent the main plasma.