Ion composition in and near the frontside boundary layer

A unique set of magnetopause crossings by the AMPTE/CCE spacecraft from near its 8.8 R(E) apogee is used to identify 13 crossings within the first two years after launch time that contain significant data intervals in the magnetosheath, boundary layer, and nearby outer magnetosphere. It is concluded that shocked solar wind or magnetosheath ions as well as ions from the outer magnetosphere overlap the boundary layer. Low-energy He(2+) as well as high charge state CNO, Si, and Fe group ions clearly overlap the boundary layer from their solar wind source. Similarly, O(+), N(+), O2(+) and NO(+) + O2(+) overlap the boundary layer from their magnetospheric source region. It is found that ion densities in the boundary layer are roughly one half those observed in the respective source regions, and that ion transport across the boundary layer is a one-way process with dawn-dusk asymmetry.