Changes in the frequency distribution of f0Es and fbEs over two solar cycles

The dependence of the occurrence probabilities of ionosonde sporadic-E parameters f₀E_s and f_bE_s on probing frequency is analyzed for wintertime for day and night for two Southern Hemisphere stations. The ionosonde data indicate that significant changes have taken place over the period 1958–1983 suggesting that E_s has become increasingly dense and also less patchy.