IMAGE EUV observation of radially bifurcated plasmaspheric features: First observations of a possible standing ULF waveform in the inner magnetosphere M.L. Adrian Center for Space Plasma and Aeronomic Research, University of Alabama in Huntsville, Huntsville, AL 35899 D.L. Gallagher and L.A. Avanov Science Directorate, SD50, NASA/Marshall Space Flight Center, Huntsville, AL 35812 We present EUV observations of the plasmasphere-plasmapause from 19:38-22:11 UT on 28 June 2000 characterized by the presence of bifurcated radial enhancements of the He+ plasma distribution in the nighside sector. These features remain stable throughout the period of observation and are found co-rotate at 67% of the expected rate. Two-dimensional simulation of the plasmasphere assuming the presence of field lines resonances at L = 1.8 and 2.5 suggest that the organization of the outer plasmasphere and plasmapause is the result convective motion driven by a standing ULF-wave. Preliminary analysis of ground-based magnetometer data provided by the IMAGE magnetometer network during the period of EUV observation indicates the presence of a discrete spectrum of field line resonances extending down to 0.68-mHz. _______________ Journal of Geophysical Research, 109 (A1), A01203, doi:10.1029/2003JA009974, 2004