Evidence for a Further Ionospheric Ledge Above the F2Region

On ionospheric investigations by coherent radiowaves emitted from artificial Earth satellites

“…An important fact which follows from Figure 16, as well as from the data of other EAS experiments which are plotted on Figure 17 (see [8,10,14,85]), consists in the following: under certain conditions the mean profiles N~(Z) have an additional maximum above the altitude ZmF2 of the main electron density maximum NinE2. Similar N (Z) maxima have also been observed at various altitudes above ZmF2 by the EAS Ariel [109] experiments and in ionosphere investigations by the radiowave incoherent scatter method [26,100]. However the mean profiles N,(Z) in Figures 16 and 17 should be considered thus-that in the altitude intervals, where they occur, increased electron density values were more often observed in these experiments.…”

Peculiar features of ionospheric F3 layer during prolonged solar minimum (2007–2009)

“…The phenomenon of F 3 layer is known for more than half a century from ground based ionosonde observations as a stratification of F 2 layer [Sen, 1949;Ratcliffe, 1951;Skinner et al, 1954], and also from topside sounding measurements as ionization ledges [Sayers et al, 1962;Lockwood and Nelms, 1964;Raghavarao and Sivaraman, 1974;Sharma and Raghavarao, 1989]. For a long time, the stratification of F 2 layer (or the ledge) remained unexplained.…”

Equatorial ionospheric variations during geomagnetic storms

“…As is shown in Figure 5 Also, in the hellosphere [Nicolet, 1961;Hanson, 1962;Bates and Patterson, 1962], a temperature increase during geomagnetic storms [Dessler, 1959;Jacchia, 1959] may cause an additional ionization. The ledge zone above Hm•x [Sayers et al, 1962] may also play an important role (luring storms. In any event, when these excess ionizations overcome the decay process they diffuse aIong the earth's magnetic fieId Iines under the influence of gravity and pressure gradients, in a way simiIa.…”