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.

Electron‐Scale Reconnection in Three‐Dimensional Shock Turbulence

“…Panel (d) shows E ′ ⋅ J where E ′ = E + v e × B , indicating the conversion of energy from fields to particles which can occur in reconnection regions. In panels (e) and (f), we use a recently developed diagnostic based on magnetic flux transport (MFT), which has been used to diagnose reconnection sites in turbulent regions in both simulations and observations even when flow patterns are unclear (Li et al., 2021; Qi et al., 2022). For this reconnection site, the MFT velocity is calculated as $$${\mathbf{U}}_{\psi }=\frac{{E}_{M}}{{B}_{p}}\left({\hat{\mathbf{e}}}_{M}\times {\hat{\mathbf{b}}}_{p}\right),$$$ where E M is the electric field in the M direction and B p is the in‐plane ( L ‐ N plane) magnetic field.…”

“…Panel (d) shows E′ ⋅ J where E′ = E + v e × B, indicating the conversion of energy from fields to particles which can occur in reconnection regions. In panels (e) and (f), we use a recently developed diagnostic based on magnetic flux transport (MFT), which has been used to diagnose reconnection sites in turbulent regions in both simulations and observations even when flow patterns are unclear (Li et al, 2021;Qi et al, 2022). For this reconnection site, the MFT velocity is calculated as…”

Relating the Phases of Magnetic Reconnection Growth to the Temporal Evolution of X-line Structures in a Collisionless Plasma

“…We include a diagram in figure 9 to illustrate the main characteristics of field evolution and energy transport during each phase of reconnection growth. In future studies, it may be useful to examine time-evolving magnetic energy transport and accumulation not through Poynting flux, but through quantities such as magnetic flux transport (MFT) 22,23 , which measure the velocity of magnetic energy transport rather than energy flux. Such comparisons may make it easier to directly compare magnetic energy transport to plasma velocities in the outflow and examine what conditions cause the reconnection process to stabilize.…”

Extended magnetic reconnection in kinetic plasma turbulence

“…The MFT method has been demonstrated to accurately identify reconnection in 2D gyrokinetic turbulence [39] and 3D shock turbulence [52] simulations. Recent MMS observations have further demonstrated the accuracy of MFT statistically, having directly measured MFT signatures for active reconnection throughout Earth's magnetosphere [47].…”

“…Magnetic flux transport. Recently, a novel method based on magnetic flux transport (MFT), which is inherent to reconnection, has been considered in simulations and observations of plasma turbulence [39,47]. This method is based on the definition of reconnection as the transport of magnetic flux across magnetic separatrices that intersect at an X-line [48].…”