Ionospheric F2 region: Variability and sudden stratospheric warmings

The ionospheric F-2 region is known to show a large day-to-day and hour-to-hour variability. Some of this variability has recently being linked to sudden stratospheric warmings (SSWs). We therefore investigate the extent of ionospheric changes following SSWs of 2007, 2008, and 2009 using ionosonde data from six different stations in the Asian zone, thus covering a broad latitudinal range from 23.2 degrees N to 45.1 degrees N. We find that ionospheric F-2 region shows some significant perturbations soon after the start of the warming. However, characteristics of these perturbations vary from event to event and from station to station. We also examine the data on equatorial electrojet strength (EEJ) during these warmings and find that there are significant changes in the EEJ strength during the SSW events. A counter electrojet coincident with the start of warming was observed for the SSW event of 2008. We then compare this SSW-linked variability observed by us to the normal day-to-day and hour-to-hour variability seen in the ionospheric data. We find that even during times when there are no SSWs and solar and magnetic indices are quite stable and close to their minimum values, the ionospheric variability is comparable to the variability attributed to these warmings. Further, it seems to us that it is difficult to quantify with precision the changes in f(o)F(2), as well as in the ionospheric response times involved, following these events.