Successive interacting coronal mass ejections: How to create a perfect storm?

TL;DR

This study uses 3-D magnetohydrodynamic simulations to analyze how successive coronal mass ejections interact and amplify space weather effects at Earth, highlighting the importance of CME orientation and chirality for forecasting geomagnetic storms.

Contribution

It introduces a parametric simulation approach to study CME-CME interactions and their impact on space weather, emphasizing the role of CME orientation and magnetic reconnection.

Findings

CME interactions can lead to extreme space weather conditions at Earth.

CME orientation and handedness significantly influence magnetic flux conservation and geomagnetic impact.

Identifying CME chirality in the solar corona can improve early storm forecasting.

Abstract

Coronal mass ejections (CMEs) are the largest type of eruptions on the Sun and the main driver of severe space weather at the Earth. In this study, we implement a force-free spheromak CME description within 3-D magnetohydrodynamic simulations to parametrically evaluate successive interacting CMEs within a representative heliosphere. We explore CME-CME interactions for a range of orientations, launch time variations and CME handedness and quantify their geo-effectiveness via the primary solar wind variables and empirical measures of the disturbance storm time index and subsolar magnetopause standoff distance. We show how the interaction of two moderate CMEs between the Sun and the Earth can translate into extreme conditions at the Earth and how CME-CME interactions at different radial distances can maximise different solar wind variables that induce different geophysical impacts. In particular, we demonstrate how the orientation and handedness of a given CME can have a significant impact on the conservation and loss of magnetic flux, and consequently B$_z$, due to magnetic reconnection with the interplanetary magnetic field. This study thus implicates identification of CME chirality in the solar corona as an early diagnostic for forecasting geomagnetic storms involving multiple CMEs.