Figure 1. The average seasonal and local time variations in ln(N/N₀), at Argentine Islands (65⁰ S) for 1971-1981, taken from Rodger et al. (1989).

Figure 2. The equatorial extent of the “composition bulge” at 1200 UT, for equivalent storms in the northern hemisphere for a) summer, b) winter, and c) equinox conditions.

Figure 3a. Numerical simulation of a period during November and December of 1997 for the winter hemisphere. The top panel shows a comparison of the observed f₀F2 and the monthly median. The middle panel is a comparison between the observed and CTIM modeled ratio of storm to quiet foF2 values. The lower panel shows the variations in the geomagnetic index a_p.

Figure 3b. Same as Figure 3a except for summer hemisphere.

Figure 4. Time history of the a_p index over a five day interval from June 5^th 1981, and the evolution of the ionosphere at mid-latitude over South America.

Figure 5. Filter shape, F(t), representing the relationship between the geomagnetic index a_p and the ionospheric storm-time response at summer mid-latitudes.

Figure 6. The seasonal/latitude response of the storm-to-quiet foF2 as a function of filtered a_p, X(t₀).

Figure 7. Observed and empirical model FoF2 ratios for the event that occurred on November 22/23 at two sites, Rome in the northern hemisphere (winter) and Grahamstown in the southern hemisphere (summer).

Figure 8. Illustration of the local time dependence in the residual of the foF2 storm-to-quiet ratio.