Identifying magnetic reconnection events using the FOTE method

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Theoretically, magnetic reconnection—the process responsible for solar flares and magnetospheric substorms—occurs at the X‐line or radial null in the electron diffusion region (EDR). However, whether this theory is correct is unknown, because the radial null (X‐line) has never been observed inside the EDR due to the lack of efficient techniques and the scarcity of EDR measurements. Here we report such evidence, using data from the recent MMS mission and the newly developed First‐Order Taylor Expansion (FOTE) Expansion technique. We investigate 12 EDR candidates at the Earth's magnetopause and find radial nulls (X‐lines) in all of them. In some events, spacecraft are only 3 km (one electron inertial length) away from the null. We reconstruct the magnetic topology of these nulls and find it agrees well with theoretical models. These nulls, as reconstructed for the first time inside the EDR by the FOTE technique, indicate that the EDR is active and the reconnection process is ongoing.

Section: Multicase Analysesmentioning

confidence: 84%

Evidence of Magnetic Nulls in Electron Diffusion Region

Cao

et al. 2019

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“…The First-Order Taylor Expansion (FOTE) method, developed recently by Fu et al (2015Fu et al ( , 2016, provides a good opportunity to address this issue. The First-Order Taylor Expansion (FOTE) method, developed recently by Fu et al (2015Fu et al ( , 2016, provides a good opportunity to address this issue.…”

Section: 1029/2018gl081708mentioning

confidence: 99%

Electron Distribution Functions Around a Reconnection X‐Line Resolved by the FOTE Method

Wang

Liu

et al. 2019

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Using data from the MMS mission and the First‐Order Taylor Expansion (FOTE) method, here we reveal electron distribution functions around a reconnection X‐line at the Earth's magnetopause. We find cigar distribution of electrons in both the magnetosphere‐side and magnetosheath‐side inflow regions, isotropic distribution of electrons at the separatrix, and loss of high‐energy electrons in the antiparallel direction in the magnetosheath‐side inflow region. We interpret the formation of cigar distribution in the inflow regions using the Fermi mechanism—as suggested in previous simulations, the loss of high‐energy electrons in the magnetosheath side using the parallel electric fields—which evacuate electrons to escape the diffusion region along the antiparallel direction, and the isotropic distribution at the separatrix using the pitch angle scattering by whistler waves—which exist frequently at the separatrix. We also find that the electron distribution functions can change rapidly (within 60 ms) from isotropic to cigar as the spacecraft moves slightly away from the separatrix.

“…The reported magnetic islands were observed from shock surface to the vicinity of the magnetopause, had a spatial size of a few tens of ion inertial length in the magnetosheath, and were characterized by a density depletion and magnetic field compression [Karimabadi et al, 2014, Figures 6, 9, and 13]. In spacecraft data, distinguishing between magnetic islands and flux ropes is not obvious (magnetic islands can indeed be seen as the 2-D version of 3-D flux ropes [e.g., Fu et al, 2015Fu et al, , 2016). In spacecraft data, distinguishing between magnetic islands and flux ropes is not obvious (magnetic islands can indeed be seen as the 2-D version of 3-D flux ropes [e.g., Fu et al, 2015Fu et al, , 2016).…”

Section: Introductionmentioning

confidence: 99%

MMS observations of ion‐scale magnetic island in the magnetosheath turbulent plasma

Huang

Sahraoui

Retinò

et al. 2016

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In this letter, first observations of ion‐scale magnetic island from the Magnetospheric Multiscale mission in the magnetosheath turbulent plasma are presented. The magnetic island is characterized by bipolar variation of magnetic fields with magnetic field compression, strong core field, density depletion, and strong currents dominated by the parallel component to the local magnetic field. The estimated size of magnetic island is about 8 di, where di is the ion inertial length. Distinct particle behaviors and wave activities inside and at the edges of the magnetic island are observed: parallel electron beam accompanied with electrostatic solitary waves and strong electromagnetic lower hybrid drift waves inside the magnetic island and bidirectional electron beams, whistler waves, weak electromagnetic lower hybrid drift waves, and strong broadband electrostatic noise at the edges of the magnetic island. Our observations demonstrate that highly dynamical, strong wave activities and electron‐scale physics occur within ion‐scale magnetic islands in the magnetosheath turbulent plasma.