Abstract
One of the grand challenges in heliophysics is the characterization 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 modeling. Accordingly, we present in this work the analysis of two CMEs that erupted from the Sun on April 28, 2012. We follow their eruption and early evolution using remote‐sensing data, finding indications of CME–CME interaction, and then analyze 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.
Highlights
Coronal mass ejections (CMEs; e.g., Webb & Howard, 2012) are spectacular eruptions of magnetic fields and plasma that are regularly launched from the Sun throughout the heliosphere
By propagating the following measurements at Saturn at the resulting trailing edge speed (387 km⋅s−1 ), good agreement between the two data sets continues to be displayed roughly until the ejecta trailing edge at Venus and the start of the identified interaction region at Saturn. This would suggest that the original ejecta resulting from the interaction of CME1 and CME2 may be linked to approximately the first third of the flux rope interval identified at Saturn, and that the full ejecta may on the other hand correspond to a merged interaction regions (MIRs), which as mentioned in the Introduction is a dominating structure in the outer heliosphere
We have analyzed the eruption and evolution of two CMEs (CME1 and CME2) that left the Sun on April 28, 2012 just a few hours apart. After observing their early evolution through the solar corona, we found indications of interaction in Heliospheric Imagers (HI) imagery, and we eventually identified signatures of a single ejecta at the in-situ locations that we considered (Venus, Earth, and Saturn), suggesting that the two eruptions had merged
Summary
Coronal mass ejections (CMEs; e.g., Webb & Howard, 2012) are spectacular eruptions of magnetic fields and plasma that are regularly launched from the Sun throughout the heliosphere. It is unclear to which extent 1D in-situ measurements are representative of the global CME structure (e.g., Al-Haddad et al, 2011; Owens et al, 2017), mainly because of distortions (e.g., Manchester et al, 2004; Owens, 2008; Savani et al, 2010) and/or the particular sampling distance with respect to the CME nose and central axis (e.g., Cane et al, 1997; Kilpua et al, 2011; Marubashi & Lepping, 2007) As they propagate through the solar corona and interplanetary space, CMEs are known to experience deflections and rotations
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