Possible contribution of the OGO-5 ion composition measurement to an extension of IRI for the plasmasphere

Orbiting Geophysical Observatory 5 (OGO 5) magnetospheric ion-composition data (H+, He+ and O+) from an ion spectrometer [Sharp, IEE Trans. in Geosci. Elect. V, GE-7, 93, 1969] have been retrieved from old magnetic tapes archived at the National Space Science Data Center (NSSDC). The highly compressed binary format was converted into a user-friendly ASCII for-mat and these data have now been made available from the NSSDC (http://nssdcftp.gsfc.nasa.gov). Additionally we have recovered the ephemeris information. Using these data we have inves-tigated altitude/field line distributions (derived by statistically analyzing all the data) of all measured ions inside the plasmasphere. We discuss a possible extension of the current ion composition model in the International Reference Ionosphere (IRI) above its current upper boundary of validity (2500km). We also compare the locations of the OGO-5 H+ and He+ plasmapause positions.