Observation of a Fully-formed Forward--Reverse Shock Pair Due to the Interaction Between Two Coronal Mass Ejections at 0.5 au

TL;DR

This paper reports the first direct observation of a forward-reverse shock pair caused by the interaction of two coronal mass ejections at 0.5 au, revealing complex shock dynamics and energetic particle activity.

Contribution

It provides the first in-situ evidence of a fully-formed forward-reverse shock pair resulting from CME interaction, supported by remote and in-situ observations.

Findings

First direct observation of a CME-induced shock pair at 0.5 au

Enhanced energetic particles and magnetic reconnection observed

Complex shock signatures at 1 au indicating CME interaction

Abstract

We report direct observations of a fast magnetosonic forward--reverse shock pair observed by Solar Orbiter on March 8, 2022 at the short heliocentric distance of 0.5 au. The structure, sharing some features with fully-formed stream interaction regions (SIRs), is due to the interaction between two successive coronal mass ejections (CMEs), never previously observed to give rise to a forward--reverse shock pair. The scenario is supported by remote observations from the STEREO-A coronographs, where two candidate eruptions compatible with the in-situ signatures have been found. In the interaction region, we find enhanced energetic particle activity, strong non-radial flow deflections and evidence of magnetic reconnection. At 1~au, well radially-aligned \textit{Wind} observations reveal a complex event, with characteristic observational signatures of both SIR and CME--CME interaction, thus demonstrating the importance of investigating the complex dynamics governing solar eruptive phenomena.