Sounding rocket measurements of ion composition and charged particle temperatures in the topside ionosphere

The concentrations of H + , He + , and (O + + N + ) were measured as a function of altitude from 300 to 600 km by means of an ion mass spectrometer. The major constituent was found to be O + over the entire altitude range, decreasing from >99% of the total ion concentration at 300 km to 88% at 600 km. Hydrogen and helium ions were present as minor constituents increasing with altitude to 11% and ∼1%, respectively, at 600 km. At the same time, the electron and total ion concentrations and temperature were measured and compared by means of retarding potential analyzers. The ion temperature was found to increase from 1100° at 300 km to 1600° at 600 km. Electron temperatures were found to increase rather sharply in the 400‐ to 500‐km altitude range from the fairly typical value of 2500° to the very high value of 3500° at 600 km. Comparisons with the electron concentration profiles obtained from the Wallops Island ionosonde station and from the topside sounder Alouette 2 showed good agreement. Relationships among the observables and with the inferred neutral gas temperature of 1060° are discussed.