High-resolution (8000 sample s-1) data from the Polar Electric Field Instrument are analyzed for a study of ion mode solitary waves in upward current regions of the auroral zone. The primary focus of this study is the relations between velocity, maximum potential amplitude, and parallel structure width of these solitary waves (SWs). The observed SW velocities consistently lie, within error bars, between those of the H+ and O+ beams observed simultaneously by the Toroidal Imaging Mass-Angle Spectrograph (TIMAS) instrument. In addition, there is a trend that SW amplitudes are smaller when SW velocities are near the O+ beam velocity and larger when SW velocities are near the H+ beam velocity. These results are consistent with the observed ion mode SWs being a mechanism for the transfer of energy from the H+ beam to the O+ beam. A clear trend is also observed indicating larger amplitude with larger parallel spatial width. The results suggest that the observed solitary waves are a rarefactive ion mode associated with the ion two-stream instability. ¿ 2001 American Geophysical Union