Minor Ion Composition in CME-Related Solar Wind

Abstract

Elemental and ionic charge state composition measurements play an important role in the identification of different structures in the solar wind. Solar wind associated with coronal mass ejections (CMEs) frequently exhibit helium and minor ion (Z > 2) elemental abundances (relative to protons) that are enhanced compared to nominal solar wind values. Another aspect of CME-related composition is an apparent enrichment of elemental abundances relative to photospheric values for elements with low (< 10 eV) first ionization potentials, the so-called FIP effect. Charge states of CME-related solar wind usually indicate hotter than normal coronal conditions at the solar wind freezing-in site. However, the charge state signature varies among different events, and a high charge state signature within an event does not preclude the simultaneous presence of lower charge states that paradoxically suggest lower coronal temperatures. The compositional distinctions are not as prevalent in CME-related solar wind observed at higher heliographic latitudes, as measured by the Ulysses spacecraft. At these higher latitudes, the observed CME-related ionization temperatures and the He/H abundance ratios are closer to the prevailing polar coronal hole solar wind values.