Variability correction for the five airglow line classes and the airglow continuum (analysed at 0.543 μm) of the sky model. Upper panels: the variability is shown as a function of the bimonthly period (1 = Dec./Jan., ..., 6 = Oct./Nov.), time bin (third of the night), and solar activity measured by the solar radio flux. Lower panels: for bimonthly period and time bin, the relative uncertainties of the variability correction are displayed.