On the electron distribution function in the F region and airglow enhancements during HF modification experiments

The variation with height and plasma frequency of the distribution function of ambient electrons (EDF) in the F region ionosphere during high-power, H F radio wave modification experiments is discussed. It is shown that the de viation of the EDF from a Maxwellian distribution (MD) in the high energy, >2 eV, range may be quite significant (decreasing by a factor of 2 to 5) de pending on the background parameters. As a result, the cooling and excitati on rates are reduced with respect to a MD calculation. This, for example, c an improve agreement of the model based on excitation by heated thermal ele ctrons with the observations of 630.0 nm airglow during HF modification exp eriments.