The Inhomogeneity of Composition Along the Magnetic Cloud Axis

Abstract

Coronal mass ejections (CMEs) are one of the most energetic explosions in the solar system. It is generally accepted that CMEs result from eruptions of magnetic flux ropes, which are dubbed as magnetic clouds (MCs) in interplanetary space. The composition (including the ionic charge states and elemental abundances) is determined prior to and/or during CME eruptions in the solar atmosphere and does not alter during MC propagation to 1 AU and beyond. It has been known that the composition is not uniform within a cross section perpendicular to the MC axis, and the distribution of ionic charge states within a cross section provides us an important clue to investigate the formation and eruption processes of flux ropes due to the freeze-in effect. The flux rope is a three-dimensional magnetic structure intrinsically, and it remains unclear whether the composition is uniform along the flux rope axis as most MCs are only detected by one spacecraft. In this study, we report an MC that was observed by Advanced Composition Explorer at ∼1 AU during March 4–6, 1998, and Ulysses at ∼5.4 AU during March 24–28, 1998, sequentially. At these times, both spacecraft were located around the ecliptic plane, and the latitudinal and longitudinal separations between them were ∼2.2° and ∼5.5°, respectively. It provides us an excellent opportunity to explore the axial inhomogeneity of flux rope composition, as both spacecraft almost intersected the cloud center at different sites along its axis. Our study shows that the average values of ionic charge states exhibit significant difference along the axis for carbon, and the differences are relatively slight but still obvious for charge states of oxygen and iron as well as the elemental abundances of iron and helium. Besides the means, the composition profiles within the cloud measured by both spacecraft also exhibit some discrepancies. We conclude that the inhomogeneity of composition exists along the cloud axis.

The Solar Cycle Dependence of In Situ Properties of Two Types of Interplanetary CMEs during 1999–2020

“…First, flux rope structures are dismissed during propagation in the heliosphere. Second, the spacecraft only crosses the flank regions of ICMEs and does not detect the flux rope structures, which should be more clear at the center of ICMEs, considering that the ICMEs may have core and envelop structures (Reinard 2008;Song et al 2021b;Zhai et al 2022). If the probabilities of the above situations for NFCs are the same as that for FCs, the present statistical results suggest that NFCs are all associated with flux rope structures on the Sun.…”

Comparison of Helium Abundance between ICMEs and Solar Wind near 1 AU

“…It is widely accepted that CMEs result from eruption of magnetic flux ropes (e.g., Chen 2011), which can form prior to (e.g., Cheng et al 2011;Patsourakos et al 2013) and during (e.g., Song et al 2014;Jiang et al 2021) eruptions. The composition (including both the charge states and elemental abundances of heavy ions) pro-vides an important avenue to analyze their eruption process (Lepri & Zurbuchen 2004;Lynch et al 2011;Gruesbeck et al 2011Gruesbeck et al , 2012Song et al 2015Song et al , 2016Song et al , 2017Song & Yao 2020;Gu et al 2020;Song et al 2021b), and supports that more CMEs come from active regions around solar maximum, whose heavy ions possess higher charge states and enriched relative abundances (Song et al 2021a).…”

Comparison of Ion–Proton Differential Speed between Interplanetary Coronal Mass Ejections and Solar Wind near 1 au

“…One important research field about ICMEs and solar wind is their elemental abundance of heavy ions, including the absolute abundance (relative to hydrogen) and relative abundance (generally relative to oxygen; e.g., Lepri et al 2013;Zurbuchen et al 2016;Owens 2018;Song & Yao 2020;Song et al 2021b). We can acquire the elemental abundance of ICMEs directly by means of the measurement of spacecraft near 1 au, with which to infer their plasma origin.…”