Interactions between Coronal Mass Ejections Viewed in Coordinated Imaging and In Situ Observations

TL;DR

This study uses coordinated imaging and in situ data to analyze CME-CME interactions, revealing how such interactions affect shock dynamics and space weather predictions.

Contribution

It provides detailed observational evidence of CME interactions near 1 AU, highlighting their impact on shock behavior and space weather forecasting.

Findings

CME interactions can lead to shock merging and acceleration.

Merged CME fronts can significantly alter shock strength.

Interactions influence particle acceleration and space weather predictions.

Abstract

The successive coronal mass ejections (CMEs) from 2010 July 30 - August 1 present us the first opportunity to study CME-CME interactions with unprecedented heliospheric imaging and in situ observations from multiple vantage points. We describe two cases of CME interactions: merging of two CMEs launched close in time and overtaking of a preceding CME by a shock wave. The first two CMEs on August 1 interact close to the Sun and form a merged front, which then overtakes the July 30 CME near 1 AU, as revealed by wide-angle imaging observations. Connections between imaging observations and in situ signatures at 1 AU suggest that the merged front is a shock wave, followed by two ejecta observed at Wind which seem to have already merged. In situ measurements show that the CME from July 30 is being overtaken by the shock at 1 AU and is significantly compressed, accelerated and heated. The interaction between the preceding ejecta and shock also results in variations in the shock strength and structure on a global scale, as shown by widely separated in situ measurements from Wind and STEREO B. These results indicate important implications of CME-CME interactions for shock propagation, particle acceleration and space weather forecasting.