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.
Highlights
Coronal mass ejections (CMEs) are an energetic explosive phenomenon in the solar atmosphere [1,2,3,4], and they are called interplanetary coronal mass ejections (ICMEs) after leaving the corona
The researchers of the solar physics community have reached a consensus that CMEs result from eruptions of magnetic flux ropes (MFRs), which refer to a volumetric current channel with the helical magnetic field lines wrapped around the central axial field [10, 11]
We report an intriguing event, in which an magnetic clouds (MCs) was observed by Advanced Composition Explorer (ACE) at ∼1 AU during March 4–6, 1998, and Ulysses at ∼5.4 AU during March 24–28, 1998
Summary
Coronal mass ejections (CMEs) are an energetic explosive phenomenon in the solar atmosphere [1,2,3,4], and they are called interplanetary coronal mass ejections (ICMEs) after leaving the corona. The Grad–Shafranov (GS) reconstruction [51, 52] demonstrated that the MC axis oriented in an approximate east–west direction with the axis direction at Ulysses being tilted slightly away from that at ACE, and both spacecraft almost intersected the MC center [53] This implies that the two spacecraft cross the MC along two trajectories resembling the black and red arrows, respectively, and provide us an excellent opportunity to explore whether the composition is uniform along the axis. The SWICS instruments on board both spacecraft [58, 59] offer the composition of heavy ions
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