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Abstract Electron-only magnetic reconnection was first detected by the Magnetospheric Multiscale (MMS) mission in Earth’s turbulent magnetosheath. Its prevalence in kinetic-scale turbulence has attracted great interest in heliophysics, but also revealed a great challenge in identifying it in turbulence, where electron flows are often complex. The magnetic flux transport (MFT) method is an innovative method to identify active reconnection in numerical simulations and in situ observations of turbulent plasmas. Here we extend this method to distinguish between electron-only and ion-coupled reconnection. The coupling of magnetic field motion with plasma flows in the diffusion regions sets distinct scales in the MFT velocity. While both forms of reconnection satisfy the MFT signature for active reconnection as MFT inflows and outflows at an X-line, the specific electron-only MFT signature is only an electron-scale MFT outflow along the current sheet normal direction, whereas the specific ion-coupled signature is a two-scale, outer-ion-and-inner-electron-scale MFT outflow in the electron diffusion region, which evolves into a single ion-scale in the ion diffusion region. These signatures are verified in a simulation of gyrokinetic turbulence. The dependence of the MFT outflow on the distance downstream from the X-lines also agrees well with the framework of magnetic field–plasma flow coupling. The new MFT signatures provide a clear and reliable tool for investigating electron-only reconnection in turbulence, independent of the development of electron outflows. They are directly applicable to kinetic and fluid simulations, and have potential application to observations of diffusion region crossings by spacecraft missions such as MMS.
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Magnetic Flux Transport Identification of Active Reconnection: MMS Observations in Earth’s Magnetosphere
Abstract Magnetic reconnection plays an important role in converting energy while modifying field topology. This process takes place under varied plasma conditions during which the transport of magnetic flux is intrinsic. Identifying active magnetic reconnection sites with in situ observations is challenging. A new technique, Magnetic Flux Transport (MFT) analysis, has been developed recently and proven in numerical simulation for identifying active reconnection efficiently and accurately. In this study, we examine the MFT process in 37 previously reported electron diffusion region (EDR)/reconnection-line crossing events at the day-side magnetopause and in the magnetotail and turbulent magnetosheath using Magnetospheric Multiscale measurements. The coexisting inward and outward MFT flows at an X-point provides a signature that magnetic field lines become disconnected and reconnected. The application of MFT analysis to in-situ observations demonstrates that MFT can successfully identify active reconnection sites under complex varied conditions, including asymmetric and turbulent upstream conditions. It also provides a higher rate of identification than plasma outflow jets alone. MFT can be applied to in situ measurements from both single- and multi-spacecraft missions and laboratory experiments.
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- Award ID(s):
- 2000222
- PAR ID:
- 10363218
- Publisher / Repository:
- DOI PREFIX: 10.3847
- Date Published:
- Journal Name:
- The Astrophysical Journal Letters
- Volume:
- 926
- Issue:
- 2
- ISSN:
- 2041-8205
- Format(s):
- Medium: X Size: Article No. L34
- Size(s):
- Article No. L34
- Sponsoring Org:
- National Science Foundation
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