Determination of the O⁺(²P) ionization frequency using satellite airglow and neutral composition data and its implications on the EUV solar flux

Simultaneous measurements of the O + (²D ‐ ²P) emission at 7319‐30Å and the atomic oxygen density in the optically thin region of the atmosphere offer a straightforward means of determining the photoionization frequency, I ∞ , for the production of O + (²P) ions. The ionization frequency is found to be 4.7 × 10 −8 sec −1 ±30% on June 8, 1974 and 3.4 × 10 −8 sec −1 ±30% on December 17, 1975. The wavelength dependent solar flux intensity in the relevant spectral region was also measured June 8, 1974 on the same spacecraft (Atmosphere Explorer‐C). A calculation of I ∞ using this solar flux and currently accepted values of the photoionization excitation cross sections gives a value of 4.9 × 10 −8 sec −1 , thus confirming the measured solar EUV flux.