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At least 181 records · Page 10
All sourcesNASA NTRSDOE OSTI
NASA NTRS2014

Onset of Reconnection in the near Magnetotail: PIC Simulations

Using 2.5-dimensional particle-in-cell (PIC) simulations of magnetotail dynamics, we investigate the onset of reconnection in two-dimensional tail configurations with finite Bz. Reconnection onset is preceded by a driven phase, during which magnetic flux is added to the tail at the high-latitude boundaries, followed by a relaxation phase, during which the configuration continues to respond to the driving. We found a clear distinction between stable and unstable cases, dependent on deformation amplitude and ion/electron mass ratio. The threshold appears consistent with electron tearing. The evolution prior to onset, as well as the evolution of stable cases, are largely independent of the mass ratio, governed by integral flux tube entropy conservation as imposed in MHD (magnetohydrodynamics). This suggests that ballooning instability in the tail should not be expected prior to the onset of tearing and reconnection. The onset time and other onset properties depend on the mass ratio, consistent with expectations for electron tearing. At onset,we found electron anisotropies T⊥⁄ T∥ (bottom tail divided by parallel tail) equals 1.1-1.3, raising growth rates and wavenumbers. Our simulations have provided a quantitative onset criterion that is easily evaluated in MHD simulations, provided the spatial resolution is sufficient. The evolution prior to onset and after the formation of a neutral line does not depend on the electron physics, which should permit an approximation by MHD simulations with appropriate dissipation terms.

PIC↗
DOE OSTI2022

Lower‐Hybrid Wave Structures and Interactions With Electrons Observed in Magnetotail Reconnection Diffusion Regions

Abstract We investigate waves close to the lower‐hybrid frequency in 12 magnetotail reconnection electron diffusion region (EDR) events with guide field levels of near‐zero to 30%. In about half of the events, the wave vector has a small component along the current sheet normal, consistent with known lower‐hybrid drift wave properties, but the perpendicular magnetic field fluctuations can be comparable or greater than the parallel component, a feature unique to the waves inside and adjacent to EDRs. Another new wave property is that the wave vector has a significant component along the current sheet normal in some events and completely along the normal for one event. In 1/4 of the events, the term has a significant contribution to the wave electric field, possibly a feature of lower‐hybrid waves more likely to exist in the diffusion region than further away from the X‐line. Electron temperature variations are correlated with the wave potential, due to wave electric field acceleration and crossings at the corrugated separatrix region with different amounts of mixing between reconnection inflowing and outflowing populations. The latter also leads to the anti‐correlation between parallel and perpendicular temperature components. Using four‐spacecraft measurements, the magnetic field line twisting is demonstrated by the correlated fluctuations in and . The lower‐hybrid wave in the EDR of weak guide field reconnection may be generated near separatrices and penetrate to the mid‐plane or locally generated, and the latter possibility is beyond the prediction of previous reconnection simulations.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2026

Statistical Study of Energy Dissipation in Magnetic Structures During Turbulent Reconnection in the Earth's Magnetotail

Magnetic reconnection is a ubiquitous plasma phenomenon that plays a critical role in particle heating and energization. During reconnection, the topology of magnetic field rearranges, depositing energy into the surrounding plasma through bulk flow, thermal heating, or non-thermal particle acceleration. While the pathways of this transformation from magnetic energy into kinetic have been studied extensively in recent years through theoretical or case-by-case observations, comprehensive statistical studies remain limited. In this paper, we present a statistical investigation using data from the Magnetospheric Multiscale (MMS) mission, and detail the particle energization mechanisms in magnetic structures found near reconnecting regions in turbulent Earth's magnetotail. We find that electrons with motion perpendicular to the magnetic field dominate $\vec{j}$ ⋅ $\vec{E}$ dissipation. In contrast to the conventional picture of unidirectional energy transfer to particles by laminar two-dimensional (2D) reconnection, we find that energy exchange within magnetic structures during turbulent reconnection tends to be bidirectional with only a small positive bias from electromagnetic fields to particles. Specific electron energization mechanisms are quantified, including those due to parallel electric field, Fermi energization from curvature drift, betatron heating from magnetic field inhomogeneity, and polarization drift.

Wang, Rachel [Princeton University, NJ (United Sta↗
DOE OSTI2022

Theory, observations, and simulations of kinetic entropy in a magnetotail electron diffusion region

In this work, we examine velocity-space kinetic entropy, a spatially local measure of entropy for systems out of thermal equilibrium, during an encounter of an electron diffusion region at a magnetic reconnection site in Earth’s magnetotail by the Magnetospheric Multiscale (MMS) mission. We start by generalizing the theory of kinetic entropy to the case of non-uniform velocity space grids and transforming the equations into spheri- cal energy coordinates useful to experimental plasma detectors. The theory is then applied to MMS data and compared to particle-in-cell simulations of reconnection. We demonstrate that the entropy-based non-Maxwellianity measure from the MMS data is of sufficiently high precision to reliably identify non-Maxwellian distributions and therefore the measurements when kinetic effects are most significant. By comparing two different non-Maxwellian measures, we show that total entropy density suffers from “information loss” because it lacks a dependence on the velocity space grid, and so has lost information about how well a distribution function is resolved. Local velocity-space kinetic entropy density recovers this information. We quantify information loss and argue that the considerations needed to minimize it are crucial for instruments designed to measure distribution functions in situ.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1971

Magnetospheric substorms in the distant magnetotail observed by Imp 3.

Study of variations of the magnetic field and plasma sheet in the distant magnetotail (20 to 40 earth radii) during magnetospheric substorms on the basis of the Imp 3 magnetic-field and particle data. Depending on the locations of the satellite with respect to the boundary of the plasma sheet, the variations differ greatly. However, the present results and the results of other workers give a clear indication of an increase of the magnitude of the field outside the plasma sheet and of the simultaneous ?thinning' of the plasma sheet during an early phase of substorms. At about the maximum epoch or during the recovery phase of substorms, the plasma sheet expands and appears to be inflated to at least the presubstorm level. Furthermore, a large excessive flux of the magnetic (approximately equal to Z component) field, as compared with the flux of the original dipole field, appears across the neutral sheet.

Meng, C. I.↗
NASA NTRS1973

The magnetotail and substorms

The tail plays a very active and important role in substorms. Magmetic flux eroded from the dayside magnetosphere is stored here. As more and more flux is transported to the magnetotail and stored, the boundary flares more, the field strength in the tail increases, and the currents strengthen and move closer to the earth. Further, the plasma sheet thins and the magnetic flux crossing the neutral sheet lessens. The experimental evidence for these processes is discussed and a phenomenological or qualitative model of the substorm sequence is presented. In this model, the flux transport is driven by the merging of the magnetospheric and interplanetary magnetic fields. During the growth phase of substorms the merging rate on the dayside magnetosphere exceeds the reconnection rate in the neutral sheet.

Russell, C. T.↗
NASA NTRS1974

Magnetic field configuration in the magnetotail near 60 earth radii

The magnetic field line configuration in the geomagnetic tail near 60 earth radii is examined on the basis of nearly 3 years of magnetometer data from the lunar-orbiting Explorer 35 satellite. The magnetotail field line characteristics inside the plasma sheet and in the high-latitude tail, i.e., outside the plasma sheet, are separately examined. In the high-latitude tail the magnetic field lines systematically diverge in both longitudinal (east-west) and latitudinal (north-south) directions; the divergence angle between field lines near the dusk flank and those near the dawn flank is about 14 deg, but the divergence along the Z direction is only about 8 deg. The degree of divergence is found to be greater in the evening side than in the morning side and greater in the northern tail than in the southern tail. Inside the plasma sheet the field lines deviate by about 19 deg from the sun-earth line, and the spatial distribution of the field line deviation does not have any systematic tendency.

Meng, C.-I.↗
NASA NTRS1976

Jupiter's magnetotail as the source of interplanetary Jovian MeV electrons observed at earth

The source of interplanetary Jovian MeV electron enhancements observed at earth is found to be Jupiter's magnetotail. If an average solar wind speed of 400 km/sec is assumed, the main region of emission extends from about 1.0 AU downstream from Jupiter to about 2.0 AU beyond the planet. (If a value of 350 km/sec is assumed, it extends from about 0.4 AU to about 1.2 AU.) Individual 'active' zones are about 0.2 AU in length. It is proposed that interplanetary magnetic field line connection with the tail is the mechanism providing the Jovian electrons observed at earth.

Pesses, M. E.↗
NASA NTRS1976

The magnetosphere of Venus - Evidence for a boundary layer and a magnetotail

Mariner 5 magnetic field data collected during its flyby of Venus are evaluated in the light of reexamination of Venera data and in the context of present knowledge on the interaction of the solar wind with the earth. Attention is focused on an analysis of 4 phenomenological regions: magnetosheath, boundary layer, tail, and upstream waves. Enough evidence is revealed for a boundary layer beginning in the dayside ionosphere. The study affirms the possibility that Venus has an intrinsic magnetotail; the key elements of this identification are the positions of the Mariner 5, Venera 4 and Venera 9 magnetopause crossings and the agreements of the polarity of the field during the Mariner 5 and Venera 9 wake traversals with the direction of the implied Venera 4 dipole moment.

Russell, C. T.↗