Calculated ionospheric variations due to changes in the solar EUV flux measured by the AEROS spacecraft

Abstract

The solar EUV radiation from the whole solar disk for wavelengths between 15.5 and 103.76 nm was measured by the AEROS-EUV spectrometer during the period December 1972 through August 1973. These measurements show a long-term decrease in solar EUV output with decreasing solar activity, a 27-day variation, and day-to-day and other short-term fluctuations. These solar EUV flux data are used with a model of the ionospheric E- and F-regions to calculate the variation of ionospheric properties that are associated with the changes in the measured solar EUV flux. The model calculates the variations in electron and ion density, electron and ion temperature, photoelectron spectra, various airglow emission rates, and the minor neutral constituents N( 2D) , N( 4S) and NO. The results show that in general the magnitude of all ionospheric and atmospheric properties increases with increasing solar EUV flux. However, percentage changes of the calculated properties are different from each other and also from the percentage change of the measured total solar EUV energy flux. This occurs because a nonuniform variation of the solar flux with wavelength is observed over the EUV spectrum by the AEROS-EUV spectrometer and altitude-dependent aeronomic processes are sensitive to the detailed flux values within the solar EUV spectrum.