Trends in the ionospheric E and F regions over Europe

Continuous observations in the ionospheric E and F regions have been regularly carried out since the ®fties of this century at many ionosonde stations. Using these data from 31 European stations long-term trends have been derived for di€erent parameters of the ionospheric E layer (h¢ E, foE), F1 layer (foF1) and F2 layer (hmF2, foF2). The detected trends in the E and F1 layers (lowering of the E region height h¢E; increase of the peak electron densities of the E and F1 layers, foE and foF1) are in qualitative agreement with model predictions of an increasing atmospheric greenhouse e€ect. In the F2 region, however, the results are more complex. Whereas in the European region west of 30° E negative trends in hmF2 (peak height of the F2 layer) and in the peak electron density (foF2) have been found, in the eastern part of Europe (east of 30° E) positive trends dominate in both parameters. These marked longitudinal di€erences cannot be explained by an increasing greenhouse e€ect only, here probably dynamical e€ects in the F2 layer seem to play an essential role.