Are There Differences Between Solar Wind and Solar Composition?
1.D.1 Elemental Fractionation. The situation is different for elements and isotopes. In situ spacecraft instruments observe differences in element ratios between the photosphere and the solar wind. From systematics and theoretical work [e.g. Marsch et al., 1995], it is well-established that elemental fractionation depends on: (1) first ionization time (FIT), i.e. the time required for an atom in the solar atmosphere to become ionized. FIT is a function of the atomÃs first ionization potential (FIP) and solar physical conditions. The primary fractionation is a relative enhancement of low-FIT (easily ionized) elements as a group compared with high-FIT elements. (2) ion charge and mass. Once an atom is ionized, it is subjected to Coulomb drag in the flowing plasma, which depends on both charge and mass. This is smaller than the FIT effect (both observationally and theoretically) and (3) solar wind regime. 1.D.1.a Solar Wind Regimes. These refer to the different sources of the solar-wind.
