Latitudinal variation of F2-region response to geomagnetic disturbance

The effect of geomagnetic storms on the F2 region was studied by calculating the deviation, ΔfoF2, of foF2 during 40 magnetic storms, ranging from moderate (Dst < −50 nT) to very intense (Dst < −200 nT) of the 21st solar cycle. In order to study the variation of storm-time foF2 with latitude, season and storm strength, ionosonde data were obtained from eight stations spanning a latitudinal range of +60-−60°. The stations chosen lay in a narrow longitudinal range of 140-151°, so that local time difference between the stations is practically negligible. The features exhibited by positive and negative phases were essentially different. The storm time ΔfoF2 clearly exhibited a latitudinal variation and this variation were found to be coupled with the seasonal variation. As for the variation with storm intensity, though ΔfoF2 was found to vary even between two storms of almost equal intensity, the amplitude of a positive or negative phase, |ΔfoF2max| showed a distinct upper limit for each intensity category of storms.