Comparisons of inferred total plasmasphere content with measured plasma density profiles

The first comparisons are reported between values of the total plasmasphere cold plasma density as deduced from whistler‐determined equatorial plasma profiles and as inferred from beacon satellite group delay methods. We find the two independently determined total content values to be equivalent to within about 25% for 3 days and to within a factor of <2 for 2 days, when data are presently available. We conclude that it is difficult to deduce the position of the plasmapause from group delay total content data without a separate measure of the plasma density at the base of the plasmasphere (∼2000‐km altitude).