Solar Wind and Heavy Ion Properties of Interplanetary Coronal Mass Ejections

Abstract

Magnetic field and plasma properties of the solar wind measured in near-Earth space are a convolution of coronal source conditions and in-transit processes which take place between the corona and near-Earth space. Elemental composition and heavy ion charge states, however, are not significantly altered during transit to Earth and thus such properties can be used to diagnose the coronal source conditions of the solar wind observed in situ. We use data from the Advanced Composition Explorer (ACE) spacecraft to statistically quantify differences in the coronal source properties of interplanetary coronal mass ejections (ICMEs). Magnetic clouds, ICMEs which contain a magnetic flux-rope signature, display heavy ion properties consistent with significantly hotter coronal source regions than non-cloud ICMEs. Specifically, magnetic clouds display significantly elevated ion charge states, suggesting they receive greater heating in the low corona. Further dividing ICMEs by speed, however, shows this effect is primarily limited to fast magnetic clouds and that in terms of heavy ion properties, slow magnetic clouds are far more similar to non-cloud ICMEs. As such, fast magnetic clouds appear distinct from other ICME types in terms of both ion charge states and elemental composition. ICME speed, rather ICME type, correlates with helium abundance and iron charge state, consistent with fast ICMEs being heated through the more extended corona. Fast ICMEs also tend to be embedded within faster ambient solar wind than slow ICMEs, though this could be partly the result of in-transit drag effects. These signatures are discussed in terms of spatial sampling of ICMEs and from fundamentally different coronal formation and release processes.