Observations of an extreme storm in interplanetary space caused by successive coronal mass ejections

TL;DR

This study investigates an extreme space weather storm caused by interacting coronal mass ejections, revealing how successive eruptions and solar wind conditions can amplify space weather events.

Contribution

It uncovers the formation mechanism of an extreme storm through multi-point observations, highlighting the role of CME interactions and solar wind preconditioning.

Findings

Interaction of two CMEs led to extreme magnetic field enhancement.

Fast transit time due to preconditioning of solar wind.

Novel features in the formation of extreme space weather events.

Abstract

Space weather refers to dynamic conditions on the Sun and in the space environment of the Earth, which are often driven by solar eruptions and their subsequent interplanetary disturbances. It has been unclear how an extreme space weather storm forms and how severe it can be. Here we report and investigate an extreme event with multi-point remote-sensing and in-situ observations. The formation of the extreme storm showed striking novel features. We suggest that the in-transit interaction between two closely launched coronal mass ejections resulted in the extreme enhancement of the ejecta magnetic field observed near 1 AU at STEREO A. The fast transit to STEREO A (in only 18.6 hours), or the unusually weak deceleration of the event, was caused by the preconditioning of the upstream solar wind by an earlier solar eruption. These results provide a new view crucial to solar physics and space weather as to how an extreme space weather event can arise from a combination of solar eruptions.