Research Fig.2:
Ionospheric electron spectra for various heights computed with a local equilibrium model.
The shapes of the spectra for energies greater than about 0.5 Ry show good agreement with in-situ satellite measurements of electron fluxes in the ionosphere (apart from the curve for 800 km where the neglection of plasma transport effects in the theoretical model becomes apparent).
The strong decrease of the number of electrons for small energies reflects directly the increase of the
Radiative Recombination Cross Section with decreasing energy, whilst the peak around 0.5 Ry for the lower heights is caused by energy degradation of electrons due to inelastic collisions (electron impact ionization of atomic oxygen and helium, and excitation of vibrational states of molecular nitrogen).
There is thus no indication of the electrons becoming thermalized at energies of around 0.01 Rydberg (as suggested by traditional LTE ionospheric models), and the additional peak in the measured fluxes for energies smaller than 0.5 Ry (allegedly showing the bulk background of thermal electrons) is therefore most likely due to a contamination with 'spacecraft photoelectrons'.
(See also the
Home Page for a general quantitative discussion of the various collision processes in plasmas and the validity of LTE and related assumptions.)
