THE RESPONSE OF THE IONOSPHERIC F2-LAYER TO GEOMAGNETIC-ACTIVITY - ANANALYSIS OF WORLDWIDE DATA

The 'disturbed/quiet' ratio of the peak electron density NmF2 is expre ssed 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 d egrees S. The local-time and seasonal Variations broadly resemble thos e 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. t err. Phys. 51, 851-866). The worldwide data show consistent latitudina l patterns, with NmF2 enhanced in local winter as compared to equinox and summer. The AC variations are consistent in phase (maximum at 15-2 0 LT) except in the magnetic equatorial region, where the phase is alm ost reversed. A 'long-term' effect is found, in which the data for dif ferent periods (sunspot cycles) show markedly different DC levels. The results are interpreted in terms of the 'composition change' theory o f 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 deri ved from the MSIS-90 model, and with results from CTIPM, a coupled the rmosphere-ionosphere model. Copyright (C) 1996 Elsevier Science Ltd.