Note on the cause of ionization in the F-region

Recent rocket data on the intensity of the solar 303.8 A HeII line at the 140-km and 212-km level of the upper atmosphere are utilized to investigate the possibility that this radiation may be largely responsible for the heating and ionization effects in the F-region. Electron densities at 140 km and at 212 km are computed on the basis that the 303.8 A photons ionize oxygen atoms. The computed results compare favorably with observed values of electron densities measured at these heights on ionograms taken at the same time as the rocket flight which yielded the 303.8 A intensity data.