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Abstract In 1972, early August, a series of interplanetary shocks were observed in the heliosphere from 0.8 to 2.2 au. These shocks were attributed to a series of brilliant flares and plasma clouds since at that time coronal mass ejections (CMEs) and their interplanetary counterparts (ICMEs) were unknown to the scientific community. This paper aims to reinterpret the interplanetary data in light of the current understanding about interplanetary transients and to track the evolution of the ICMEs, taking advantage of the alignment of Pioneers 9 and 10 spacecraft. For this purpose, we reanalyze in situ data from these two Pioneers and also from Heos, Prognoz 1 and 2, and Explorer 41 spacecraft searching for ICMEs and high-speed streams. Then we assemble the interplanetary transients and solar activity and analyze the propagation of the ejections through the heliosphere. The evolution of four ICMEs and a high-speed stream from a low-latitude coronal hole is followed using the multipoint in situ observations. The first three ICMEs show clear signatures of ICME–ICME interaction in the interplanetary medium, suggesting the first observations of an ICME which developed into an ICME-in-the-sheath. For a non-perturbed ICME event, we obtain the evolution parameter,ζ, related to the local expansion of ICMEs, getting similar values for Pioneer 9 (ζ= 0.80) and Pioneer 10 (ζ= 0.78). These results support previous findings ofζbeing independent of the heliocentric distance and the magnetic field strength decreasing asr−2ζ.
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Multipoint Observations of the Dynamics at an ICME Sheath–Ejecta Boundary
Abstract The radial evolution of interplanetary coronal mass ejections (ICMEs) is dependent on their interaction with the ambient medium, which causes ICME erosion and affects their geoefficiency. Here, an ICME front boundary, which separates the confined ejecta from the mixed, interacted sheath–ejecta plasma upstream, is analyzed in a multipoint study examining the ICME at 1 au on 2020 April 20. A bifurcated current sheet, highly filamented currents, and a two-sided jet were observed at the boundary. The two-sided jet, which was recorded for the first time for a magnetic shear angle <40°, implies multiple (patchy) reconnection sites associated with the ICME erosion. The reconnection exhaust exhibited fine structure, including multistep magnetic field rotation and localized structures that were measured only by separate Cluster spacecraft with the mission inter-spacecraft separation of 0.4–1.6RE. The mixed plasma upstream of the boundary with a precursor at 0.8 au lacked coherency at 1 au and exhibited substantial variations of southward magnetic fields over radial (transverse) distances of 41–237RE(114RE). This incoherence demonstrates the need for continuous (sub)second-resolution plasma and field measurements at multiple locations in the solar wind to adequately address the spatiotemporal structure of ICMEs and to produce accurate space weather predictions.
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- Award ID(s):
- 2033563
- PAR ID:
- 10469600
- Publisher / Repository:
- DOI PREFIX: 10.3847
- Date Published:
- Journal Name:
- The Astrophysical Journal
- Volume:
- 956
- Issue:
- 2
- ISSN:
- 0004-637X
- Format(s):
- Medium: X Size: Article No. 131
- Size(s):
- Article No. 131
- Sponsoring Org:
- National Science Foundation
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