Intercomparison of various measurements of thermal plasma densities at and near the plasmapause

Four methods of investigating the thermal plasma density near the plasmapause have been intercompared for the period 1 to 15 July 1972. These methods are whistlers, the double floating probe on Explorer 45, three IMP I plasma wave signatures and observations made aboard both Prognoz 1 and Prognoz 2. Explorer 45 data have provided new information on the plasmapause bulge which, during this period, occurs at 16 L.T. This displacement from the accepted time of 18 L.T. or even later is substantiated by the Russian satellites. All methods give the result that the plasmapause is found at an electron number density somewhere between 20 and 120 cm−3 or, alternatively, at 60 cm−3, to within a factor of 2.