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Three-Dimensional Ion-Scale Magnetic Flux Rope Generated from Electron-Scale Magnetopause Current Sheet: Magnetospheric Multiscale Observations
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  • Hiroshi Hasegawa,
  • Richard E. Denton,
  • Kyunghwan Dokgo,
  • Kyoung-Joo Hwang,
  • Takuma Nakamura,
  • James L Burch
Hiroshi Hasegawa
Institute of Space and Astronautical Science, JAXA

Corresponding Author:hase@stp.isas.jaxa.jp

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Richard E. Denton
Dartmouth College
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Kyunghwan Dokgo
Southwest Research Institute
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Kyoung-Joo Hwang
Southwest Research Institute
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Takuma Nakamura
Institute of Physics, University of Graz
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James L Burch
Southwest Research Institute
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We present in-depth analysis of three southward-moving meso-scale (ion- to magnetohydrodynamic-scale) flux transfer events (FTEs) and subsequent crossing of a reconnecting electron-scale current sheet (ECS), which were observed on 8 December 2015 by the Magnetospheric Multiscale spacecraft near the subsolar magnetopause under southward and duskward magnetosheath magnetic field conditions. Our aims are to understand the generation mechanism of ion-scale magnetic flux ropes (ISFRs) and to reveal causal relationship among magnetic structures of the ECS, electromagnetic energy conversion, and kinetic processes in magnetic reconnection layers. Magnetic field reconstruction methods show that a flux rope with a length of about one ion inertial length existed and was growing in the ECS, supporting the idea that ISFRs can be generated from secondary magnetic reconnection in ECS. Grad-Shafranov reconstruction applied to the three FTEs shows that the FTE flux ropes had axial orientations similar to that of the ISFR in the ECS. This suggests that these FTEs also formed through the same secondary reconnection process, rather than multiple X-line reconnection at spatially separated locations. Four-spacecraft observations of electron pitch-angle distributions and energy conversion rate suggest that the ISFR had three-dimensional magnetic topology and secondary reconnection was patchy or bursty. Previously reported positive and negative values of , with magnitudes much larger than expected for typical magnetopause reconnection, were seen in both magnetosheath and magnetospheric separatrix regions of the ISFR. Many of them coexisted with bi-directional electron beams and intense electric field fluctuations around the electron gyrofrequency, consistent with their origin in separatrix activities.