Kinematics of Interacting CMEs of September 25 and 28, 2012

TL;DR

This study analyzes the 3D kinematics and interaction of two CMEs from September 2012 using multiple modeling techniques, revealing their collision dynamics and impact on geomagnetic activity.

Contribution

It applies combined stereoscopic and heliospheric reconstruction methods to accurately characterize CME interactions and collision properties, a novel approach for this event.

Findings

CME collision was nearly elastic based on restitution coefficient

Different angular extents significantly affect kinematic estimates

Interaction contributed to a major geomagnetic storm

Abstract

We have studied two Coronal Mass Ejections (CMEs) that occurred on September 25 and 28, 2012 and interacted near the Earth. By fitting the Graduated Cylindrical Shell (GCS) model on the SECCHI/COR2 images and applying the Stereoscopic Self-Similar Expansion (SSSE) method on the SECCHI/HI images, the initial direction of both the CMEs is estimated to be west of the Sun-Earth line. Further, the three-dimensional (3D) heliospheric kinematics of these CMEs have been estimated using Self-Similar Expansion (SSE) reconstruction method. We show that use of SSE method with different values of angular extent of the CMEs, leads to significantly different kinematics estimates for the CMEs propagating away from the observer. Using the estimated kinematics and true masses of the CMEs, we have derived the coefficient of restitution for the collision which is found to be close to elastic. The in situ measurements at 1 AU show two distinct structures of interplanetary CMEs, heating of the following CME, as well as ongoing interaction between the preceding and the following CME. We highlight the signatures of interaction in remote and in situ observations of these CMEs and the role of interaction in producing a major geomagnetic storm.