Electron Inflow Velocities and Reconnection Rates at Earth's Magnetopause and Magnetosheath

Burch, J. L.; Webster, J.; Hesse, Michael; Genestreti, K. J.; Denton, R. E.; Phan, T. D.; Hasegawa, Hiroshi; Cassak, P. A.; Torbert, R. B.; Giles, B. L.; Gershman, D. J.; Ergun, R. E.; Russell, C. T.; Strangeway, R. J.; Contel, O. Le; Pritchard, K. R.; Marshall, A.; Hwang, K-J; Dokgo, K.; Fuselier, S. A.; Chen, Li‐Jen; Wang, S.; Swisdak, M.; Drake, J. F.; Argall, M. R.; Trattner, K. J.; Paschmann, G.

doi:10.1029/2020gl089082

Cited by 26 publications

(36 citation statements)

References 37 publications

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“…Note that the equality between the first and the last terms is consistent with the high-cadence observation of Magnetospheric Multiscale Mission (MMS) 60 . For m i /m e = 400 as in the simulation, B 2 xe =B 2 xi ' 0:05.…”

Section: Resultssupporting

confidence: 83%

“…This has been ascertained from the abundance of data from the MMS mission, which has unprecedented spatial and temporal resolutions. In particular, 2D simulations have done an excellent job reproducing detailed reconnection dynamics [34][35][36]60,79 . Nevertheless, it remains an open question to explore whether fast reconnection can proceed in Nature without eventually forming a dominating kinetic current sheet in three-dimensional plasmas.…”

Section: Discussionmentioning

confidence: 99%

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First-principles theory of the rate of magnetic reconnection in magnetospheric and solar plasmas

Liu

Cassak

et al. 2022

Commun Phys

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The rate of magnetic reconnection is of the utmost importance in a variety of processes because it controls, for example, the rate energy is released in solar flares, the speed of the Dungey convection cycle in Earth’s magnetosphere, and the energy release rate in harmful geomagnetic substorms. It is known from numerical simulations and satellite observations that the rate is approximately 0.1 in normalized units, but despite years of effort, a full theoretical prediction has not been obtained. Here, we present a first-principles theory for the reconnection rate in non-relativistic electron-ion collisionless plasmas, and show that the same prediction explains why Sweet-Parker reconnection is considerably slower. The key consideration of this analysis is the pressure at the reconnection site (i.e., the x-line). We show that the Hall electromagnetic fields in antiparallel reconnection cause an energy void, equivalently a pressure depletion, at the x-line, so the reconnection exhaust opens out, enabling the fast rate of 0.1. If the energy can reach the x-line to replenish the pressure, the exhaust does not open out. In addition to heliospheric applications, these results are expected to impact reconnection studies in planetary magnetospheres, magnetically confined fusion devices, and astrophysical plasmas.

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Section: Resultssupporting

confidence: 83%

Section: Discussionmentioning

confidence: 99%

First-principles theory of the rate of magnetic reconnection in magnetospheric and solar plasmas

Liu

Cassak

et al. 2022

Commun Phys

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“…Because the magnetic flux is likely to expand somewhat as it extends upward from the chromospheric footpoints to the current sheet, the inflow speed may be expected to be about 100 km s −1 ; this agrees with the almost universally found reconnection rate of order 10% (e.g. Birn et al 2001;Daughton et al 2014;Nakamura et al 2018;Burch et al 2020;Chen et al 2020) for a 1,000 km s −1 Alfvén speed. Assuming an outflow scale of 10 Mm, together with the observed UV brightening time, implies an outflow speed of 100-500 km s −1 , which also agrees with both simulations (Guidoni et al 2016b) and coronal observations (e.g.…”

Section: Discussionsupporting

confidence: 80%

Correlated Spatiotemporal Evolution of Extreme-Ultraviolet Ribbons and Hard X-rays in a Solar Flare

Naus,

Qiu,

DeVore

et al. 2021

Preprint

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We analyze the structure and evolution of ribbons from the M7.3 SOL2014-04-18T13 flare using ultraviolet (UV) images from IRIS and SDO/AIA, magnetic data from SDO/HMI, hard X-ray (HXR) images from RHESSI, and light curves from Fermi /GBM, in order to infer properties of coronal magnetic reconnection. As the event progresses, two flare ribbons spread away from the magnetic polarity inversion line. The width of the newly brightened front along the extension of the ribbon is highly intermittent in both space and time, presumably reflecting non-uniformities in the structure and/or dynamics of the flare current sheet. Furthermore, the ribbon width grows most rapidly in regions exhibiting concentrated non-thermal HXR emission, with sharp increases slightly preceding the HXR bursts. The light curve of the ultraviolet emission matches the HXR light curve at photon energies above 25 keV. In other regions the ribbon-width evolution and light curves do not temporally correlate with the HXR emission. This indicates that the production of non-thermal electrons is highly nonuniform within the flare current sheet. Our results suggest a strong connection between the production of non-thermal electrons and the locally enhanced perpendicular extent of flare ribbon fronts, which in turn reflects inhomogeneous structure and/or reconnection dynamics of the current sheet. Despite this variability, the ribbon fronts remain nearly continuous, quasi-one-dimensional features. Thus, although the reconnecting coronal current sheets are highly structured, they remain quasi-two-dimensional and the magnetic energy release occurs systematically, rather than stochastically, through the volume of reconnecting magnetic flux.

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“…The reconnection electric field 𝐸 𝑧0 , which is optimized and assumed to be constant in the EMHD reconstruction, is 1.0 mV/m, which is comparable to 0.3 mV/m expected for the dimensionless reconnection rate 0.1 in the present case and those estimated for previously reported magnetopause EDR events (Burch et al, 2020;Hasegawa et al, 2017). However, we show in sections 3.3, 4.1, and 4.2 that the present ECS probably involved 3D dynamics and time-dependent or localized energy conversion processes; the measured electric field component 𝐸 𝑧EMHD was not stable at all.…”

Section: Fr1 Fr2 Fr3supporting

confidence: 84%

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

Hasegawa

Denton

Dokgo

et al. 2022

Preprint

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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.

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Electron Inflow Velocities and Reconnection Rates at Earth's Magnetopause and Magnetosheath

Cited by 26 publications

References 37 publications

First-principles theory of the rate of magnetic reconnection in magnetospheric and solar plasmas

First-principles theory of the rate of magnetic reconnection in magnetospheric and solar plasmas

Correlated Spatiotemporal Evolution of Extreme-Ultraviolet Ribbons and Hard X-rays in a Solar Flare

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

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