Ion composition in an IBC class II aurora. 1. Measurements

A positive ion mass spectrometer was included in a Black Brant rocket pay load fired from Poker Flat, Alaska, on March 16, 1972, in the Ice Cap 72 program. Measurements were obtained between 100 and 145 km on ascent and down to 72 km on descent during a diffuse IBC class II auroral event. Within the 1- to 38-amu mass range of the instrument the following species (listed in order of decreasing concentrations) were measured in the E region: NO+, O2+, O+, N2+, 16O18O+, N+, Mg+, and Na+ along with the contaminants OH+, H2O+, and H3O+, which made up less than or about 1% of the total ionization. The D region water cluster ions H5O2+ and H3O+ appeared at 84 km on the downleg and dominated below 81 km. Ion-electron densities were 2–4×105 cm−3 between 110 and 145 km. Measurement uncertainties and possible sources of the contaminant ions are discussed.