Temporal evolution at a fixed geometric height of z = 1200 km. Top: total Ca number density n_Ca,total and relative level populations n_i / n_total. Middle: net radiative transition rates P_r   ij for the b-f transitions between the bound levels and the continuum together with the overall sum . Bottom: the involved radiative rates R_ij and R_ji in comparison to the density of free electrons n_el. The Ca ii-iii ionisation fraction χ_Ca (grey dotted line), the gas temperature (grey dashed line), and the inversed relaxation timescale (grey solid line) are shown in all panels as reference. The rates for the transitions from the bound levels 1 − 5 to the continuum (i = 6) are divided by the total Ca number densities. Positive rates indicate ionisation, negative rates recombination.