Ionospheric ion composition deduced from VLF observations

VLF observations from the Alouette satellites have provided information on the ion composition of the ionosphere. This is derived from two sources: noise bands with a lower frequency cutoff at the lower hybrid resonance (LHR) frequency, and ion whistlers. The LHR frequency depends on the harmonic mean mass of the ionic constituents. Ion whistlers provide good measurements of the relative abundances of protons and helium ions, as well as the proton density and on occasion, proton temperatures.