On Understanding the Nature of Collision of Coronal Mass Ejections Observed by \textit{STEREO}

TL;DR

This study analyzes the collision dynamics of two coronal mass ejections using 3D reconstruction, revealing factors influencing whether their collision is elastic, inelastic, or super-elastic, with implications for space weather modeling.

Contribution

It introduces a comprehensive 3D analysis of CME collisions, quantifies uncertainties, and explores conditions leading to different collision types, which is novel in CME collision studies.

Findings

Larger expansion speed of the following CME increases super-elastic collision probability.

Relative approaching speed lower than sum of expansion speeds favors super-elastic collisions.

Inelastic collisions are more probable when considering observational uncertainties.

Abstract

Our study attempts to understand the collision characteristics of two coronal mass ejections (CMEs) launched successively from the Sun on 2013 October 25. The estimated kinematics, from three-dimensional (3D) reconstruction techniques applied to observations of CMEs by SECCHI/Coronagraphic (COR) and Heliospheric Imagers (HIs), reveal their collision around 37 $R_\sun$ from the Sun. In the analysis, we take into account the propagation and expansion speeds, impact direction, angular size as well as the masses of the CMEs. These parameters are derived from imaging observations, but may suffer from large uncertainties. Therefore, by adopting head-on as well as oblique collision scenarios, we have quantified the range of uncertainties involved in the calculation of the coefficient of restitution for expanding magnetized plasmoids. Our study shows that the comparatively large expansion speed of the following CME than that of the preceding CME, results in a higher probability of super-elastic collision. We also infer that a relative approaching speed of the CMEs lower than the sum of their expansion speeds increases the chance of super-elastic collision. The analysis under a reasonable errors in observed parameters of the CME, reveals the larger probability of occurrence of an inelastic collision for the selected CMEs. We suggest that the collision nature of two CMEs should be discussed in 3D, and the calculated value of the coefficient of restitution may suffer from a large uncertainty.