The normal state of the F2 ionospheric layer at high latitudes

The use of monthly median values to determine the normal level of the undis turbed F2 layer, leads often to inconsistent results regarding the type of ionospheric disturbance and quietness as well. Recently Belehaki et al. (20 00) proposed an hourly local ionospheric index f(n)F2 to define the normal level of the F2 layer at middle latitudes. In this paper we apply the f(n)F 2 index to observations from a high latitude station, where geomagnetic act ivity strongly influence the temporal and spatial behaviour of the ionosphe ric layers, for investigating and testing the usefulness of the f(n)F2 inde x on a planetary scale. From the analysis that follows, it was revealed tha t during intervals of low magnetospheric activity, f(n)F2 index shows a ver y good fit to the observed f(o)F2 parameter, comparing to the monthly media n f(o)F2 behaviour. On the other hand, enhanced magnetospheric activity doe s not affect the f(n)F2 index, which daily variation is a function of the s unspot number itself. In summary, the f(n)F2 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, w hich for the needs of this work it was approached as a function of the aa-i ndex for middle latitudes, whereas the AE-index was used for amoral latitud es. (C) 2001 Elsevier Science Ltd. All rights reserved.