Abstract
The intensity of the southward component of the magnetic field (Bs) carried by Interplanetary Coronal Mass Ejections (ICMEs) is one of the most critical parameters in causing extreme space weather events, such as intense geomagnetic storms. In this work, we investigate three typical ICME events with extremely intense Bs in detail and present a statistical analysis of the origins of intense Bs in different types of ICMEs based on the ICME catalogue from 1995 to 2020. According to the in-situ characteristics, the ICME events with extremely high Bs are classified into three types: isolated ICMEs, multiple ICMEs, and shock-ICME interaction events with shocks inside ICMEs or shocks passing through ICMEs. By analyzing all ICME events with Bs ≥ 10nT and Bs ≥ 20nT, we find that 39.6% of Bs,mean ≥ 10nT events and 50% of Bs,mean ≥ 20nT events are associated with shock-ICME events. Approximately 35.7% of shock-ICME events have Bs,mean ≥ 10nT, which is much higher than the other two types (isoloted ICMEs: 7.2% and multiple ICMEs: 12.1%). Those results confirm that the ICMEs interaction events are more likely to carry extreme intense Bs and cause intense geomagntic storms. Only based on the in-situ observations at Earth, some interaction ICME events, such as shock-ICME interaction events with shocks passing through the preceding ICME or ICME cannibalism, could be classified as isolated ICME events. This may lead to an overestimate of the probability of ICME carrying extremely intense Bs. To further investigate such events, direct and multi-point observations of the CME propagation in the inner heliosphere from the Solar Ring Mission could be crucial in the future.
Highlights
Interplanetary Coronal Mass Ejections (ICMEs), the interplanetary counterparts of the Coronal Mass Ejections (CMEs), are considered to be the main source of geomagnetic storms, especially the intense geomagnetic storms [1,2,3,4,5,6,7,8,9]
Intense Bs have been discovered to come from a variety of ICME types, including isolated ICMEs (I-ICMEs), multiple ICMEs (M-ICMEs), shock-ICME interaction events (S-ICMEs) with shocks inside ICMEs, and S-ICMEs with shocks passed through ICMEs
We studied all the ICME events with Bs,mean ≥ 10nT from 1995 to 2020, and found that the interaction events (i.e., M-ICMEs, and S-ICMEs) can result in extremely high Bs with a higher probability
Summary
Interplanetary Coronal Mass Ejections (ICMEs), the interplanetary counterparts of the Coronal Mass Ejections (CMEs), are considered to be the main source of geomagnetic storms, especially the intense geomagnetic storms [1,2,3,4,5,6,7,8,9]. From another point of view, Shen et al [9] found that 20% of ICMEs caused intense geomagnetic storms This might be caused by the fact that ICMEs are the main sources of the southward component of the interplanetary magnetic field Shen et al [18] found that in the shock-ICME interaction event of 6–11 September 2017, the shock compression enhanced Bs inside the ICME from 10 to 30 nT In their following work, Xu et al [21] analyzed 18 moderate to intense geomagnetic storms caused by shock-ICME interaction events, showing that the shock compression can enhance the intensities of Bs in ICME by a factor of 2. We discuss the possible origins of the extreme intense Bs in the ICMEs based on the typical events anaylsis. We will present some conclusions and discussions
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