Long-term behavior of NmF2 over the Australian ionosonde stations Canberra from 1952 to 2022 (a, b) and Hobart from 1950 to 2022 (c, d). Panels a and c: yearly means of NmF2 and F30. Panels b and d: NmF2* estimates and linear models of NmF2* (until 1984) as a function of F30*. The differences between observations and corresponding linear NmF2* models, ΔNmF2, are presented in separate plots scaled at the right side. Dashed lines indicate the RMS ± error range of the linear models taken as reference.