For many years, there has been controversy over the magnitude of both
the solar EUV (0-100 nm) irradiance and 0-1 keV photoelectron flux.
The solar EUV irradiance is the primary driver of the energetics and
dynamics of the Earth’s upper atmosphere above 100 km. There are
uncertainties in theoretical photoelectron fluxes because of
uncertainties in cross sections and solar EUV irradiance. Accurate
solar EUV irradiance measurements are difficult to make because they
must be made at high altitudes and because the energetic photons
degrade the instruments that measure them. The ionization of oxygen
and nitrogen in the upper atmosphere produces energetic photoelectrons
as well as ions. Photoelectrons take approximately half the incident
photon energy in the creation of secondary ions and electrons and
airglow emissions. In recent years, the photoelectron flux has become
important because the airglow emissions are heavily used in diagnosing
variations in the upper atmosphere. This paper reexamines the
consistency of solar EUV irradiance and ionospheric photoelectron
fluxes using recent measurements.