The normal state of the F2 ionospheric layer at high latitudes

The use of monthly median values to determine the normal level of the undisturbed F2 layer, leads often to inconsistent results regarding the type of ionospheric disturbance and quietness as well. Recently Belehaki (2000) proposed an hourly local ionospheric index f_nF2 to define the normal level of the F2 layer at middle latitudes. In this paper we apply the f_nF2 index to observations from a high latitude station, where geomagnetic activity strongly influence the temporal and spatial behaviour of the ionospheric layers, for investigating and testing the usefulness of the f_nF2 index on a planetary scale. From the analysis that follows, it was revealed that during intervals of low magnetospheric activity, f_nF2 index shows a very good fit to the observed f_oF2 parameter, comparing to the monthly median f_oF2 behaviour. On the other hand, enhanced magnetospheric activity does not affect the f_nF2 index, which daily variation is a function of the sunspot number itself. In summary, the f_nF2 index can be used as a measure of the undisturbed F2 layer at middle and high latitudes as well, caution though is needed in the definition of the quiet magnetospheric intervals, which for the needs of this work it was approached as a function of the aa-index for middle latitudes, whereas the AE-index was used for auroral latitudes.