The study of topside ionospheric irregularities during geomagnetic storms in 2015

In this study, the variations of topside ionospheric irregularities during 24 geomagnetic storms with Dst ≤ −50 nT in 2015 were examined through an algorithm specifically designed to detect a significant level of ionospheric irregularities. The algorithm was developed through the use of several parameters derived from the topside total electron content (TEC) observations from GRACE, Swarm-C, and Swarm-B. The local time characteristics of the observed equatorial plasma irregularities (EPIs) were analyzed during different phases of the storms, within 30° S–30° N magnetic latitudes. By comparing its results with corresponding in-situ electron density data and the results of previous studies, the algorithm was found to be efficient. It was observed that the detected EPIs at different stages of the storm showed local time dependence. For instance, EPIs were observed during nighttimes, but took place in the daytime occasionally during the storm main phase. Furthermore, the percentage occurrence rates were most prominent during the main phase at the post-sunset sector within less than 6 h of the storm onset. On the other hand, the occurrence rates became prominent in the post-midnight/morning sector during the recovery phase and even higher than observed in the post-sunset sector. Based on these findings it was concluded that the dominant driver of the enhanced EPIs during the post-midnight/daytime sector could be associated with disturbance dynamo electric fields.