Application of ionospheric topside‐sounding results to magnetospheric physics and astrophysics

A brief review is presented to illustrate how the knowledge and experience gained from investigations of ionospheric topside‐sounder ionograms has benefited scientific research beyond the ionosphere. In particular, to the interpretation of (1) natural radio emissions from space plasmas, (2) sounder‐stimulated echoes and plasma emissions, and plasma diagnostics in planetary magnetospheres and (3) X‐ray spectra of disks around neutron stars and black holes. The relevant data are from 60 satellite years of ionospheric topside‐sounder operations by the four satellites of the International Satellites for Ionospheric Studies (ISIS) program from 1963 through 1989. Not all of these data were reduced to ionograms on 35‐mm film. An ongoing effort at the NASA Goddard Space Flight Center is producing digital topside‐sounder ionograms directly from a selected subset of the original telemetry tapes. More than 300,000 digital ionograms are now in the National Space Science Data Center at the NASA GSFC ( http://nssdc.gsfc.nasa.gov/space/isis/isis-status.html ).