ION COMPOSITION AND CHARGE-STATE OF ENERGETIC PARTICLES IN FLUX ROPESPLASMOIDS/

Measurements from the energetic particles and ion composition (EPIC) i nstrument on Geotail are used to investigate the relative abundance of different ion species at energies similar to 10 keV to 3 MeV in flux ropes or plasmoids detected at various downstream distances from simil ar to 23 R-E to similar to 190 R-E in the tail. In terms of charge sta te, we find that during encounters with these structures most of the o xygen ions are singly charged, i.e., O+ ions of ionospheric origin, wh ile most of the helium ions are doubly charged, i.e., He++ ions of sol ar wind origin. Therefore the ion species from the solar wind and the ionosphere appear to be thoroughly mixed inside flux ropes or plasmoid s, just like the ion composition in the tail outside these structures. This study also reveals a variety of changes in the abundance of iono spheric oxygen ions within flux ropes or plasmoids. These range from s imultaneous enhancements of ionospheric oxygen ions within the structu re to delayed enhancements or no significant change of ionospheric oxy gen ions throughout the entire structure. The amount of ionospheric ox ygen ions present in flux ropes or plasmoids increases with higher geo magnetic activity as gauged by the K-p index, but it shows no apparent trend with the downstream distance. The lack of consistent enhancemen t of ionospheric oxygen ions inside these structures suggests that oxy gen ions may not play a significant role in their formation.