Understanding the Twist Distribution Inside Magnetic Flux Ropes by Anatomizing an Interplanetary Magnetic Cloud

Abstract

Magnetic flux rope (MFR) is the core structure of the greatest eruptions, that is, the coronal mass ejections (CMEs), on the Sun, and magnetic clouds are posteruption MFRs in interplanetary space. There is a strong debate about whether or not a MFR exists prior to a CME and how the MFR forms/grows through magnetic reconnection during the eruption. Here we report a rare event, in which a magnetic cloud was observed sequentially by four spacecraft near Mercury, Venus, Earth, and Mars, respectively. With the aids of a uniform‐twist flux rope model and a newly developed method that can recover a shock‐compressed structure, we find that the axial magnetic flux and helicity of the magnetic cloud decreased when it propagated outward but the twist increased. Our analysis suggests that the “pancaking” effect and “erosion” effect may jointly cause such variations. The significance of the pancaking effect is difficult to be estimated, but the signature of the erosion can be found as the imbalance of the azimuthal flux of the cloud. The latter implies that the magnetic cloud was eroded significantly leaving its inner core exposed to the solar wind at far distance. The increase of the twist together with the presence of the erosion effect suggests that the posteruption MFR may have a high‐twist core enveloped by a less‐twisted outer shell. These results pose a great challenge to the current understanding on the solar eruptions as well as the formation and instability of MFRs.

Evolution of a Long‐Duration Coronal Mass Ejection and Its Sheath Region Between Mercury and Earth on 9–14 July 2013

“…A somewhat similar approach was taken in Wang et al (2018) to recover pristine CME measurements at 1 AU for an event through which an overtaking shock was propagating. In the orbit just before the arrival of the CME, there are however ∼3.5 hr of IMF measurements, and during the following 4 orbits, periods of ∼4.5, 0.5, 5.25, and 3.75 hr when MESSENGER is in the solar wind.…”

“…The physical mechanism and consequences of CME radial evolution have been primarily obtained from statistical studies (Liu et al, 2005;Winslow et al, 2015;Janvier et al, 2019) or numerical simulations (e.g., see review by Manchester et al, 2017). Although some case studies indeed show a self-similar evolution (Good et al, 2015;Good et al, 2019), others reveal a much more complex evolution, with rotation (Nieves-Chinchilla et al, 2012), reconnection occurring inside the ME (Steed et al, 2011;Winslow et al, 2016;Jian et al, 2018) and CME-CME interaction occurring en route to Earth Wang et al, 2018). Although some case studies indeed show a self-similar evolution (Good et al, 2015;Good et al, 2019), others reveal a much more complex evolution, with rotation (Nieves-Chinchilla et al, 2012), reconnection occurring inside the ME (Steed et al, 2011;Winslow et al, 2016;Jian et al, 2018) and CME-CME interaction occurring en route to Earth Wang et al, 2018).…”

“…The statistical studies often assume that the ME evolution can be modeled as quasi-self-similar, that is, with little changes in the ME internal properties beyond expansion and deceleration. Although some case studies indeed show a self-similar evolution (Good et al, 2015;Good et al, 2019), others reveal a much more complex evolution, with rotation (Nieves-Chinchilla et al, 2012), reconnection occurring inside the ME (Steed et al, 2011;Winslow et al, 2016;Jian et al, 2018) and CME-CME interaction occurring en route to Earth Wang et al, 2018). Numerical simulations may be Journal of Geophysical Research: Space Physics 10.1029/2019JA027213 limited as well, since they typically assume that the CME can be modeled using magneto-hydrodynamics, which is appropriate for the ME but typically does not reproduce the sheath region well (Lugaz et al, 2007).…”

Radial Evolution of Coronal Mass Ejections Between MESSENGER, Venus Express, STEREO, and L1: Catalog and Analysis

“…However, except for a few studies that used multipoint spacecraft observations (Burlaga et al, 1981;Cane et al, 1997;Farrugia et al, 2011;Good et al, 2015Good et al, , 2018Janvier et al, 2019;Kilpua et al, 2011;Möstl, 2015;Möstl et al, 2009;Prise et al, 2015;Wang et al, 2018;Winslow et al, 2016Winslow et al, , 2018, CME measurements are largely restricted to single-point observations in space (see also discussion in Lugaz et al, 2018). However, except for a few studies that used multipoint spacecraft observations (Burlaga et al, 1981;Cane et al, 1997;Farrugia et al, 2011;Good et al, 2015Good et al, , 2018Janvier et al, 2019;Kilpua et al, 2011;Möstl, 2015;Möstl et al, 2009;Prise et al, 2015;Wang et al, 2018;Winslow et al, 2016Winslow et al, , 2018, CME measurements are largely restricted to single-point observations in space (see also discussion in Lugaz et al, 2018).…”

“…With currently no plasma measurements at sub-1 AU heliocentric distances, we rely on models to simulate CME evolution in the inner heliosphere. In this study, we combine two distinct issues/types of research: multispacecraft measurements of the same CME with the spacecraft at the same radial distance (Burlaga et al, 1981;Kilpua et al, 2011;Möstl et al, 2009) and multispacecraft measurements of the same CME with the spacecraft at the same longitude (Farrugia et al, 2011;Good et al, 2015Good et al, , 2018Möstl, 2015;Prise et al, 2015;Wang et al, 2018;Winslow et al, 2016Winslow et al, , 2018. As a result, it is important to have multipoint observations to understand the governing physics behind CME propagation and evolution in the inner heliosphere.…”