Neutral hydrogen flux measured at 100- to 200-km altitude in an electron aurora

Neutral hydrogen fluxes were measured at altitudes of 120–200 km by a rocket payload that also measured electron and proton fluxes and vector magnetic fields. An intense electron arc (∼2 × 108 el/cm² s sr keV) was crossed, while an upper limit to the flux of 0.5- to 20-keV protons was 106/cm² s sr keV. A neutral flux of 5 × 107/cm² s sr was observed, assuming hydrogen with > 1-keV energy, with greater north-south extent than the electron flux. Its pitch angle distribution was peaked toward 90°, tending toward isotropy in the center. This is fitted to a model describing spreading of an initial proton arc above 500 km.