## Research Fig.7a:

**Theoretical ionospheric scattering coefficient** (left ordinate) due to highly excited atomic states (corresponding to the level population in

FIG.6, i.e.

** for a plasma density of N**_{p}=10^{5}cm^{-3}) for radio waves with frequencies from 820 KHz to 1.9 GHz (lower abscissa). The thick short dashed curve gives the atomic (incoherent) coefficient, whereas the thick solid curve includes an enhancement due to phase coherent ('specular') scattering. The thin solid curve shows the broadening of the n-alpha lines in units of [Hz] (right ordinate) as a function of the level number n (upper abscissa) which relates to the frequency scale through f=f

_{0}*[1/n

^{2}-1/(n+1)

^{2}] with f

_{0}=3.29*10

^{15} Hz. The points of intersection of this curve with the lines for the frequency separation of two neighbouring levels (dashed-dotted) and the frequency separation of two neighbouring lines (n-alpha, (n+1)-alpha) (long-dashed) determine the 3 different regions for the scattering coefficient.