Initial ion composition results from the Isis 2 satellite

Isis 2 satellite carried, among other ionospheric instruments, an ion mass spectrometer designed to measure the composition of the ionosphere in the mass range 1–64 amu. The satellite, in a nearly constant 1400-km orbit, was launched on April 1, 1971. Examples of data show a wide variation in ion composition from 99% H+ at night near the equator to greater than 95% O+ (and N+) in the daytime poleward of the plasmapause. Both H+ and He+ are observed to be streaming outward from the high-latitude regions with velocities of several kilometers per second (the polar wind), determined from phase shifts in roll modulation maximums between light and heavy ion species. During the August 1972 magnetic storm a unique ionosphere developed consisting of N+ as the dominant species between 55° and 80° invariant latitude (above the plasmapause) and N2+, NO+, and O2+ at the 10³-cm−3 concentration level, whereas these molecular species are usually below the detection limit of 1 ion cm−3 in quiet times at this altitude.