First Simultaneous Views of the Axial and Lateral Perspectives of a Coronal Mass Ejection

TL;DR

This study presents the first simultaneous stereoscopic observations of a coronal mass ejection from axial and lateral perspectives, revealing how their angular extents evolve over time and confirming previous measurements.

Contribution

It provides the first combined axial and lateral views of a CME, enabling direct comparison and analysis of their angular extents from multiple vantage points.

Findings

Lateral angular extent increases linearly with time.

Axial angular extent grows then slows down around 5 R_sun.

Average ratio L/D is approximately 1.6, consistent with previous single-perspective measurements.

Abstract

The different appearances exhibited by coronal mass ejections (CMEs) are believed to be in part the result of different orientations of their main axis of symmetry, consistent with a flux-rope configuration. There are observational reports of CMEs seen along their main axis (axial perspective) and perpendicular to it (lateral perspective), but no simultaneous observations of both perspectives from the same CME have been reported to date. The stereoscopic views of the telescopes onboard the $Solar$-$Terrestrial$ $Relations$ $Observatory$ (STEREO) twin spacecraft, in combination with the views from the $Solar$ $and$ $Heliospheric$ $Observatory$ (SOHO) and the $Solar$ $Dynamics$ $Observatory$ (SDO), allow us to study the axial and lateral perspectives of a CME simultaneously for the first time. In addition, this study shows that the lateral angular extent ($L$) increases linearly with time, while the angular extent of the axial perspective ($D$) presents this behavior only from the low corona to $\approx\,$5 $R_{\odot}$, where it slows down. The ratio $L/D \approx\,$1.6 obtained here as the average over several points in time is consistent with measurements of $L$ and $D$ previously performed on events exhibiting only one of the perspectives from the single vantage point provided by SOHO.