The response of the ionospheric F2-layer to geomagnetic activity: An analysis of worldwide data

The 'disturbed/quiet' ratio of the peak electron density NmF2 is expressed in terms of 'mean' (DC) and 'local time' (AC) variations for over 20 years' data from each of 53 stations between 70 degrees N and 80 degrees S. The local-time and seasonal Variations broadly resemble those found for South Atlantic/Antarctic stations by Wrenn et al. (1987, J. atmos. terr. Phys. 49, 901-913) and Rodger et al. (1989, J. atmos. terr. Phys. 51, 851-866). The worldwide data show consistent latitudinal patterns, with NmF2 enhanced in local winter as compared to equinox and summer. The AC variations are consistent in phase (maximum at 15-20 LT) except in the magnetic equatorial region, where the phase is almost reversed. A 'long-term' effect is found, in which the data for different periods (sunspot cycles) show markedly different DC levels. The results are interpreted in terms of the 'composition change' theory of F2-layer storms. They compare well with the data analysis of Prolss (1980, Rev. geophys. space. Phys. 18, 183-202), with O/N-2 ratios derived from the MSIS-90 model, and with results from CTIPM, a coupled thermosphere-ionosphere model. Copyright (C) 1996 Elsevier Science Ltd.