Articles | Volume 35, issue 1
Regular paper
30 Jan 2017
Regular paper |  | 30 Jan 2017

Understanding the variability of magnetic storms caused by ICMEs

Remi Benacquista, Sandrine Rochel, and Guy Rolland

Abstract. In this paper, we study the dynamics of magnetic storms due to interplanetary coronal mass ejections (ICMEs). We used multi-epoch superposed epoch analyses (SEAs) with a choice of epoch times based on the structure of the events. By sorting the events with respect to simple large-scale features (presence of a shock, magnetic structure, polarity of magnetic clouds), this method provides an original insight into understanding the variability of magnetic storm dynamics. Our results show the necessity of seeing ICMEs and their preceding sheaths as a whole since each substructure impacts the other and has an effect on its geoeffectiveness. It is shown that the presence of a shock drives the geoeffectiveness of the sheaths, while both the shock and the magnetic structure impact the geoeffectiveness of the ICMEs. In addition, we showed that the ambient solar wind characteristics are not the same for ejecta and magnetic clouds (MCs). The ambient solar wind upstream magnetic clouds are quieter than upstream ejecta and particularly slower. We also focused on the polarity of magnetic clouds since it drives not only their geoeffectiveness but also their temporal dynamics. South–north magnetic clouds (SN-MCs) and north–south magnetic clouds (NS-MCs) show no difference in geoeffectiveness for our sample of events. Lastly, since it is well-known that sequences of events can possibly induce strong magnetic storms, such sequences have been studied using superposed epoch analysis (SEA) for the first time. We found that these sequences of ICMEs are very usual and concern about 40 % of the ICMEs. Furthermore, they cause much more intense magnetic storms than isolated events do.

Short summary
The Earth's magnetic field creates a magnetic bulk all around it called the magnetosphere. This bulk a priori protects us from the particles coming from the sun but sometimes undergoes violent events such as interplanetary coronal mass ejections. These cause the entry of particles into the magnetosphere, which can be harmful for satellites. In this paper, we performed a statistical study to characterize the interplanetary coronal mass ejections and their ability to disturb the magnetosphere.