Three-Dimensional Ion-Scale Magnetic Flux Rope Generated from Electron-Scale Magnetopause Current Sheet: Magnetospheric Multiscale Observations

Abstract

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.

Ion‐Scale Magnetic Flux Ropes and Loops in Earth's Magnetotail: An Automated, Comprehensive Survey of MMS Data Between 2017 and 2022

“…We find that the vast majority of structures are smaller than 1 R E (with a peak around ∼0.1 − 0.2 R E , or 600 − 1200 km), comparable to the magnetotail proton gyro‐radius. Similarly sized flux ropes have been linked with so‐called secondary reconnection within thin reconnecting current sheets (e.g., Daughton et al., 2006; Dong et al., 2017; Drake et al., 2006; Eastwood et al., 2016; Hasegawa et al., 2022, 2023; Lu et al., 2020; Sun et al., 2019). Our observations of significant numbers of these ion scale structures suggest that secondary reconnection is indeed a frequent occurrence, and may play a crucial role in the dynamics of Earth's magnetotail current sheet.…”

Electron Acceleration by Interaction of Two Filamentary Currents Within a Magnetopause Magnetic Flux Rope

“…The total pressure had a peak at the FR center (Figure 1f). This is another typical signature of FRs in which the pressure force is balanced by the magnetic tension force (Hasegawa et al., 2023; Hwang et al., 2016). A striking feature inside this FR is that energetic electron (47–214 keV) fluxes increased by an order of magnitude at ∼00:25:03 UT abruptly (Figure 1b).…”

Direct Observation of Magnetic Reconnection Resulting From Interaction Between Magnetic Flux Rope and Magnetic Hole in the Earth's Magnetosheath

“…The typical observational signature of these MFRs is a bipolar variation in the magnetic field component normal to the nominal magnetopause, usually accompanied by the enhancement of the axial component. These MFRs have diameters ranging from the microscale (ion or electron inertial length) to the macroscale (tens of Earth radii), corresponding to different generation mechanisms or temporal evolution (Eastwood et al., 2016; Fear et al., 2012; H. Hasegawa et al., 2023). Of particular interest is their ultimate fate, as it affects flux and energy transfer in the magnetosphere.…”

“…Previous spacecraft observations have found direct evidence of this model, that is, convective plasma flows toward the center of MFR (H. Hasegawa et al., 2010; Hwang et al., 2018; Øieroset et al., 2011). Recent observations have revealed the occurrences of ion‐scale or electron‐scale MFRs (Z. Chen et al., 2021; Eastwood et al., 2016; H. Hasegawa et al, 2023; Teh et al., 2017; R. S. Wang et al., 2010), which are interpreted as a result of secondary reconnection (Daughton et al., 2006; Drake et al., 2006; C. Huang et al., 2011). These secondary MFRs tend to grow larger in size after they are expelled from the reconnection X‐line and travel in the exhaust region (Dong et al., 2017; H. Hasegawa et al., 2023; R. S. Wang et al., 2024).…”

“…Recent observations have revealed the occurrences of ion‐scale or electron‐scale MFRs (Z. Chen et al., 2021; Eastwood et al., 2016; H. Hasegawa et al, 2023; Teh et al., 2017; R. S. Wang et al., 2010), which are interpreted as a result of secondary reconnection (Daughton et al., 2006; Drake et al., 2006; C. Huang et al., 2011). These secondary MFRs tend to grow larger in size after they are expelled from the reconnection X‐line and travel in the exhaust region (Dong et al., 2017; H. Hasegawa et al., 2023; R. S. Wang et al., 2024). The statistical work also supports that the average size of MFRs is smaller at the subsolar magnetopause and grows as they travel toward flanks and high‐latitude magnetopause (Akhavan‐Tafti et al., 2018).…”