Magnetic Structure and Propagation of Two Interacting CMEs from the Sun to Saturn

TL;DR

This study tracks two CMEs from the Sun to Saturn, revealing their magnetic structure, interaction, and evolution using remote sensing and multi-spacecraft in-situ data, highlighting the challenges in understanding CME propagation.

Contribution

It presents a detailed multi-point analysis of two CMEs, demonstrating the importance of combined remote sensing and in-situ measurements to study their evolution and interactions.

Findings

Evidence of CME--CME interaction at Earth

Flux rope structures are consistent at Venus and Earth

Greater discrepancies in flux rope structure at Saturn

Abstract

One of the grand challenges in heliophysics is the characterisation of coronal mass ejection (CME) magnetic structure and evolution from eruption at the Sun through heliospheric propagation. At present, the main difficulties are related to the lack of direct measurements of the coronal magnetic fields and the lack of 3D in-situ measurements of the CME body in interplanetary space. Nevertheless, the evolution of a CME magnetic structure can be followed using a combination of multi-point remote-sensing observations and multi-spacecraft in-situ measurements as well as modelling. Accordingly, we present in this work the analysis of two CMEs that erupted from the Sun on 28 April 2012. We follow their eruption and early evolution using remote-sensing data, finding indications of CME--CME interaction, and then analyse their interplanetary counterpart(s) using in-situ measurements at Venus, Earth, and Saturn. We observe a seemingly single flux rope at all locations, but find possible signatures of interaction at Earth, where high-cadence plasma data are available. Reconstructions of the in-situ flux ropes provide almost identical results at Venus and Earth but show greater discrepancies at Saturn, suggesting that the CME was highly distorted and/or that further interaction with nearby solar wind structures took place before 10 AU. This work highlights the difficulties in connecting structures from the Sun to the outer heliosphere and demonstrates the importance of multi-spacecraft studies to achieve a deeper understanding of the magnetic configuration of CMEs.