## Research Fig.8a:

**Density of atoms in excited states** (thick solid curve, left ordinate) as a function of the principal quantum number n (lower abscissa)

**for a plasma density N**_{p}=10^{5}cm^{-3}. The thin solid curve gives the production rate q

_{n} (left ordinate to be multiplied by 10

^{5}) with the close dashed-dotted curve showing the initial recombinative production rate q

_{n}^{Rec} (i.e. neglecting the cascading rate q

_{n}^{casc}). The total loss frequency is given by the sum of the level decay constant A

_{n} (long-dashed curve), the collisional ionization frequency (dashed curve) and the photoionization frequency (dotted curve) where the latter corresponds to an enhanced solar radio flux as appropriate

** for a strong ('Type IV') solar burst ** (see

FIG.8b) (F

_{sol}=1). (See

FIG.6 for normal solar flux conditions, The upper abscissa shows the frequency of the n-alpha transition for the quantum number n and gives an approximate idea which levels are responsible for scattering an electromagnetic wave of a certain frequency.