Formation of a Magnetic Cloud from the Merging of Two Successive Coronal Mass Ejections

TL;DR

This study analyzes how two successive coronal mass ejections (CMEs) merge during propagation, forming a magnetic cloud with specific magnetic and plasma characteristics, based on multi-spacecraft observations.

Contribution

It provides detailed observational evidence of CME merging processes leading to magnetic cloud formation, highlighting the complete merging scenario and its signatures.

Findings

Two CMEs merged before reaching 1 AU, forming a complex ejecta.

The complex ejecta exhibits a flux rope structure consistent with a magnetic cloud.

Merged CMEs can produce MC-like signatures without interaction features.

Abstract

On 2022 March 28 two successive coronal mass ejections (CMEs) were observed by multiple spacecraft and resulted in a magnetic cloud (MC) at 1 AU. We investigate the propagation and interaction properties of the two CMEs correlated with the MC using coordinated multi-point remote sensing and in situ observations from Solar Orbiter, STEREO A, SOHO, and Wind. The first CME was triggered by a filament eruption with a high inclination angle. Roughly 9 hr later, the second CME originating from the same active region erupted with a smaller tilt angle and faster speed compared to the first one. The second CME overtook the preceding CME and formed a merged front at approximately 75 \rsun{}, which developed into a complex ejecta at 1 AU. The descending speed and low proton temperature inside the complex ejecta suggest that the two CMEs have fully merged before reaching 1 AU, leading them to begin expanding rather than compressing against each other. The complex ejecta appears to have the magnetic field and plasma signatures of an MC, although there is a discontinuity in the magnetic field implying previous interactions. The cross section of the complex ejecta, reconstructed from in situ data using a Grad-Shafranov technique, exhibits a right--handed flux rope structure. These results highlight that an MC--like complex ejecta lacking interaction features could arise from the complete merging of two CMEs.