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Hasegawa H, Denton RE, Nakamura TKM, Genestreti KJ, Phan TD, Nakamura R, Hwang K, Ahmadi N, Shi QQ, Hesse M, Burch JL, Webster JM, Torbert RB, Giles BL, Gershman DJ, Russell CT, Strangeway RJ, Wei HY, Lindqvist P, Khotyaintsev YV, Ergun RE, Saito Y. Magnetic Field Annihilation in a Magnetotail Electron Diffusion Region With Electron-Scale Magnetic Island. JOURNAL OF GEOPHYSICAL RESEARCH. SPACE PHYSICS 2022; 127:e2022JA030408. [PMID: 36248013 PMCID: PMC9541864 DOI: 10.1029/2022ja030408] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 02/22/2022] [Revised: 05/27/2022] [Accepted: 06/20/2022] [Indexed: 06/16/2023]
Abstract
We present observations in Earth's magnetotail by the Magnetospheric Multiscale spacecraft that are consistent with magnetic field annihilation, rather than magnetic topology change, causing fast magnetic-to-electron energy conversion in an electron-scale current sheet. Multi-spacecraft analysis for the magnetic field reconstruction shows that an electron-scale magnetic island was embedded in the observed electron diffusion region (EDR), suggesting an elongated shape of the EDR. Evidence for the annihilation was revealed in the form of the island growing at a rate much lower than expected for the standard X-type geometry of the EDR, which indicates that magnetic flux injected into the EDR was not ejected from the X-point or accumulated in the island, but was dissipated in the EDR. This energy conversion process is in contrast to that in the standard EDR of a reconnecting current sheet where the energy of antiparallel magnetic fields is mostly converted to electron bulk-flow energy. Fully kinetic simulation also demonstrates that an elongated EDR is subject to the formation of electron-scale magnetic islands in which fast but transient annihilation can occur. Consistent with the observations and simulation, theoretical analysis shows that fast magnetic diffusion can occur in an elongated EDR in the presence of nongyrotropic electron effects. We suggest that the annihilation in elongated EDRs may contribute to the dissipation of magnetic energy in a turbulent collisionless plasma.
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Affiliation(s)
- H. Hasegawa
- Institute of Space and Astronautical ScienceJapan Aerospace Exploration AgencySagamiharaJapan
| | - R. E. Denton
- Department of Physics and AstronomyDartmouth CollegeHanoverNHUSA
| | - T. K. M. Nakamura
- Space Research InstituteAustrian Academy of SciencesGrazAustria
- Institute of PhysicsUniversity of GrazGrazAustria
| | | | - T. D. Phan
- Space Sciences LaboratoryUniversity of CaliforniaBerkeleyCAUSA
| | - R. Nakamura
- Space Research InstituteAustrian Academy of SciencesGrazAustria
| | - K.‐J. Hwang
- Southwest Research InstituteSan AntonioTXUSA
| | - N. Ahmadi
- Laboratory for Atmospheric and Space PhysicsUniversity of ColoradoBoulderCOUSA
| | - Q. Q. Shi
- Shandong Provincial Key Laboratory of Optical Astronomy and Solar‐Terrestrial EnvironmentInstitute of Space SciencesShandong UniversityWeihaiChina
| | - M. Hesse
- NASA Ames Research CenterMoffett FieldCAUSA
| | - J. L. Burch
- Southwest Research InstituteSan AntonioTXUSA
| | | | - R. B. Torbert
- Institute of PhysicsUniversity of GrazGrazAustria
- Physics DepartmentUniversity of New HampshireDurhamNHUSA
| | - B. L. Giles
- NASA Goddard Space Flight CenterGreenbeltMDUSA
| | | | - C. T. Russell
- Department of Earth, Planetary, and Space SciencesUniversity of CaliforniaLos AngelesCAUSA
| | - R. J. Strangeway
- Department of Earth, Planetary, and Space SciencesUniversity of CaliforniaLos AngelesCAUSA
| | - H. Y. Wei
- Department of Earth, Planetary, and Space SciencesUniversity of CaliforniaLos AngelesCAUSA
| | | | | | - R. E. Ergun
- Department of Astrophysical and Planetary SciencesUniversity of ColoradoBoulderCOUSA
| | - Y. Saito
- Institute of Space and Astronautical ScienceJapan Aerospace Exploration AgencySagamiharaJapan
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2
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Magnetotail reconnection onset caused by electron kinetics with a strong external driver. Nat Commun 2020; 11:5049. [PMID: 33028826 PMCID: PMC7542433 DOI: 10.1038/s41467-020-18787-w] [Citation(s) in RCA: 41] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/03/2020] [Accepted: 09/08/2020] [Indexed: 12/02/2022] Open
Abstract
Magnetotail reconnection plays a crucial role in explosive energy conversion in geospace. Because of the lack of in-situ spacecraft observations, the onset mechanism of magnetotail reconnection, however, has been controversial for decades. The key question is whether magnetotail reconnection is externally driven to occur first on electron scales or spontaneously arising from an unstable configuration on ion scales. Here, we show, using spacecraft observations and particle-in-cell (PIC) simulations, that magnetotail reconnection starts from electron reconnection in the presence of a strong external driver. Our PIC simulations show that this electron reconnection then develops into ion reconnection. These results provide direct evidence for magnetotail reconnection onset caused by electron kinetics with a strong external driver. Magnetotail reconnection plays a crucial role in explosive energy conversion in geospace. Here, the authors show that magnetotail reconnection starts from electron reconnection in the presence of a strong external driver, which then develops into ion reconnection.
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Egedal J, Le A, Daughton W, Wetherton B, Cassak PA, Burch JL, Lavraud B, Dorelli J, Gershman DJ, Avanov LA. Spacecraft Observations of Oblique Electron Beams Breaking the Frozen-In Law During Asymmetric Reconnection. PHYSICAL REVIEW LETTERS 2018; 120:055101. [PMID: 29481157 DOI: 10.1103/physrevlett.120.055101] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/05/2017] [Indexed: 06/08/2023]
Abstract
Fully kinetic simulations of asymmetric magnetic reconnection reveal the presence of magnetic-field-aligned beams of electrons flowing toward the topological magnetic x line. Within the ∼6d_{e} electron-diffusion region, the beams become oblique to the local magnetic field, providing a unique signature of the electron-diffusion region where the electron frozen-in law is broken. The numerical predictions are confirmed by in situ Magnetospheric Multiscale spacecraft observations during asymmetric reconnection at Earth's dayside magnetopause.
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Affiliation(s)
- J Egedal
- Department of Physics, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA
| | - A Le
- Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA
| | - W Daughton
- Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA
| | - B Wetherton
- Department of Physics, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA
| | - P A Cassak
- Department of Physics and Astronomy, West Virginia University, Morgantown, West Virginia 26506, USA
| | - J L Burch
- Southwest Research Institute, San Antonio, Texas 78238, USA
| | - B Lavraud
- Institut de Recherche en Astrophysique et Planétologie, Université de Toulouse, UMR 5277, Toulouse, France
| | - J Dorelli
- Heliophysics Science Division, NASA Goddard Space Flight Center, Greenbelt, Maryland 20771, USA
| | - D J Gershman
- Heliophysics Science Division, NASA Goddard Space Flight Center, Greenbelt, Maryland 20771, USA
| | - L A Avanov
- Heliophysics Science Division, NASA Goddard Space Flight Center, Greenbelt, Maryland 20771, USA
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4
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Wang R, Nakamura R, Lu Q, Baumjohann W, Ergun RE, Burch JL, Volwerk M, Varsani A, Nakamura T, Gonzalez W, Giles B, Gershman D, Wang S. Electron-Scale Quadrants of the Hall Magnetic Field Observed by the Magnetospheric Multiscale spacecraft during Asymmetric Reconnection. PHYSICAL REVIEW LETTERS 2017; 118:175101. [PMID: 28498691 DOI: 10.1103/physrevlett.118.175101] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/17/2017] [Indexed: 06/07/2023]
Abstract
An in situ measurement at the magnetopause shows that the quadrupole pattern of the Hall magnetic field, which is commonly observed in a symmetric reconnection, is still evident in an asymmetric component reconnection, but the two quadrants adjacent to the magnetosphere are strongly compressed into the electron scale and the widths of the remaining two quadrants are still ion scale. The bipolar Hall electric field pattern generally created in a symmetric reconnection is replaced by a unipolar electric field within the electron-scale quadrants. Furthermore, it is concluded that the spacecraft directly passed through the inner electron diffusion region based on the violation of the electron frozen-in condition, the energy dissipation, and the slippage between the electron flow and the magnetic field. Within the inner electron diffusion region, magnetic energy was released and accumulated simultaneously, and it was accumulated in the perpendicular directions while dissipated in the parallel direction. The localized thinning of the current sheet accounts for the energy accumulation in a reconnection.
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Affiliation(s)
- Rongsheng Wang
- Key Laboratory of Geospace Environment, Department of Geophysics and Planetary Science, University of Science and Technology of China, Hefei 230026, China
- Space Research Institute, Austrian Academy of Sciences, Graz 8042, Austria
| | - Rumi Nakamura
- Space Research Institute, Austrian Academy of Sciences, Graz 8042, Austria
| | - Quanming Lu
- Key Laboratory of Geospace Environment, Department of Geophysics and Planetary Science, University of Science and Technology of China, Hefei 230026, China
| | | | - R E Ergun
- Department of Astrophysical and Planetary Sciences, University of Colorado Boulder, Boulder, Colorado 80303, USA
| | - J L Burch
- Southwest Research Institute, San Antonio, Texas 78238, USA
| | - Martin Volwerk
- Space Research Institute, Austrian Academy of Sciences, Graz 8042, Austria
| | - Ali Varsani
- Space Research Institute, Austrian Academy of Sciences, Graz 8042, Austria
| | - Takuma Nakamura
- Space Research Institute, Austrian Academy of Sciences, Graz 8042, Austria
| | - Walter Gonzalez
- Instituto Nacional de Pesquisas Espaciais, Sao Jose dos Campos 12227-010, Brazil
| | - Barbara Giles
- NASA, Goddard Space Flight Center, Greenbelt, Maryland 20771, USA
| | - Dan Gershman
- NASA, Goddard Space Flight Center, Greenbelt, Maryland 20771, USA
| | - Shui Wang
- Key Laboratory of Geospace Environment, Department of Geophysics and Planetary Science, University of Science and Technology of China, Hefei 230026, China
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5
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Zhang YC. Distinct characteristics of asymmetric magnetic reconnections: Observational results from the exhaust region at the dayside magnetopause. Sci Rep 2016; 6:27592. [PMID: 27270685 PMCID: PMC4897780 DOI: 10.1038/srep27592] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/07/2016] [Accepted: 05/20/2016] [Indexed: 11/25/2022] Open
Abstract
Magnetic reconnection plays a key role in the conversion of magnetic energy into the thermal and kinetic energy of plasma. On either side of the diffusion region in space plasma, the conditions for the occurrence of reconnections are usually not symmetric. Previous theoretical studies have predicted that reconnections under asymmetric conditions will bear different features compared with those of symmetric reconnections, and numerical simulations have verified these distinct features. However, to date, the features of asymmetric reconnections have not been thoroughly investigated using in situ observations; thus, some results from theoretical studies and simulations have not been tested with observations sufficiently well. Here, spacecraft observations are used in a statistical investigation of asymmetric magnetic reconnection exhaust at the dayside magnetopause. The resulting observational features are consistent with the theoretical predictions. The results presented here advance our understanding of the development of reconnections under asymmetric conditions.
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Affiliation(s)
- Y. C. Zhang
- State Key Laboratory of Space Weather, National Space Science Center, Chinese Academy of Sciences, Beijing, 100190, China
- Key Laboratory of Earth and Planetary Physics, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, 100029, China
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6
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7
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Malakit K, Shay MA, Cassak PA, Ruffolo D. New electric field in asymmetric magnetic reconnection. PHYSICAL REVIEW LETTERS 2013; 111:135001. [PMID: 24116786 DOI: 10.1103/physrevlett.111.135001] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/11/2013] [Indexed: 06/02/2023]
Abstract
We present a theory and numerical evidence for the existence of a previously unexplored in-plane electric field in collisionless asymmetric magnetic reconnection. This electric field, dubbed the "Larmor electric field," is associated with finite Larmor radius effects and is distinct from the known Hall electric field. Potentially, it could be an important indicator for the upcoming Magnetospheric Multiscale mission to locate reconnection sites as we expect it to appear on the magnetospheric side, pointing earthward, at the dayside magnetopause reconnection site.
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Affiliation(s)
- K Malakit
- Department of Physics, Mahidol University, Bangkok 10400, Thailand and Department of Physics and Astronomy, University of Delaware, Newark, Delaware 19716, USA
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8
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Aunai N, Belmont G, Smets R. Proton acceleration in antiparallel collisionless magnetic reconnection: Kinetic mechanisms behind the fluid dynamics. ACTA ACUST UNITED AC 2011. [DOI: 10.1029/2011ja016688] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Affiliation(s)
- N. Aunai
- Laboratoire de Physique des Plasmas, Ecole Polytechnique; Palaiseau France
| | - G. Belmont
- Laboratoire de Physique des Plasmas, Ecole Polytechnique; Palaiseau France
| | - R. Smets
- Laboratoire de Physique des Plasmas, Ecole Polytechnique; Palaiseau France
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9
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Lu Q, Wang R, Xie J, Huang C, Lu S, Wang S. Electron dynamics in collisionless magnetic reconnection. CHINESE SCIENCE BULLETIN-CHINESE 2011. [DOI: 10.1007/s11434-011-4440-0] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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10
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Abstract
Angelopoulos et al. (Research Articles, 15 August 2008, p. 931) reported that magnetic reconnection in Earth's magnetotail triggered the onset of a magnetospheric substorm. We provide evidence that (i) near-Earth current disruption, occurring before the conventional tail reconnection signatures, triggered the onset; (ii) the observed auroral intensification and tail reconnection are not causally linked; and (iii) the onset they identified is a continuation of earlier substorm activities.
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Affiliation(s)
- A T Y Lui
- Johns Hopkins University Applied Physics Laboratory, 11100 Johns Hopkins Road, Laurel, MD 20723-6099, USA.
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11
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Le A, Egedal J, Daughton W, Fox W, Katz N. Equations of state for collisionless guide-field reconnection. PHYSICAL REVIEW LETTERS 2009; 102:085001. [PMID: 19257745 DOI: 10.1103/physrevlett.102.085001] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/26/2008] [Indexed: 05/27/2023]
Abstract
Direct in situ observation of magnetic reconnection in the Earth's magnetotail as well as kinetic numerical studies have recently shown that the electron pressure in a collisionless reconnection region is strongly anisotropic. This anisotropy is mainly caused by the trapping of electrons in parallel electric fields. We present new equations of state for the parallel and perpendicular pressures for magnetized electrons. This model-derived here and tested against a kinetic simulation-allows a fluid description in a collisionless regime where parallel electric fields and the dynamics of both passing and trapped electrons are essential.
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Affiliation(s)
- A Le
- Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
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12
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Eastwood JP. The science of space weather. PHILOSOPHICAL TRANSACTIONS. SERIES A, MATHEMATICAL, PHYSICAL, AND ENGINEERING SCIENCES 2008; 366:4489-4500. [PMID: 18812302 DOI: 10.1098/rsta.2008.0161] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/26/2023]
Abstract
The basic physics underpinning space weather is reviewed, beginning with a brief overview of the main causes of variability in the near-Earth space environment. Although many plasma phenomena contribute to space weather, one of the most important is magnetic reconnection, and recent cutting edge research in this field is reviewed. We then place this research in context by discussing a number of specific types of space weather in more detail. As society inexorably increases its dependence on space, the necessity of predicting and mitigating space weather will become ever more acute. This requires a deep understanding of the complexities inherent in the plasmas that fill space and has prompted the development of a new generation of scientific space missions at the international level.
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Affiliation(s)
- Jonathan P Eastwood
- Space Sciences Laboratory, University of California, Berkeley, 7 Gauss Way, Berkeley, CA 94720, USA.
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13
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Angelopoulos V, McFadden JP, Larson D, Carlson CW, Mende SB, Frey H, Phan T, Sibeck DG, Glassmeier KH, Auster U, Donovan E, Mann IR, Rae IJ, Russell CT, Runov A, Zhou XZ, Kepko L. Tail reconnection triggering substorm onset. Science 2008; 321:931-5. [PMID: 18653845 DOI: 10.1126/science.1160495] [Citation(s) in RCA: 476] [Impact Index Per Article: 29.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
Magnetospheric substorms explosively release solar wind energy previously stored in Earth's magnetotail, encompassing the entire magnetosphere and producing spectacular auroral displays. It has been unclear whether a substorm is triggered by a disruption of the electrical current flowing across the near-Earth magnetotail, at approximately 10 R(E) (R(E): Earth radius, or 6374 kilometers), or by the process of magnetic reconnection typically seen farther out in the magnetotail, at approximately 20 to 30 R(E). We report on simultaneous measurements in the magnetotail at multiple distances, at the time of substorm onset. Reconnection was observed at 20 R(E), at least 1.5 minutes before auroral intensification, at least 2 minutes before substorm expansion, and about 3 minutes before near-Earth current disruption. These results demonstrate that substorms are likely initiated by tail reconnection.
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Affiliation(s)
- Vassilis Angelopoulos
- Institute of Geophysics and Planetary Physics/ESS, University of California at Los Angeles, Los Angeles, CA 90095, USA.
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14
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Kesich A, Bonde J, Egedal J, Fox W, Goodwin R, Katz N, Le A. Magnetic flux array for spontaneous magnetic reconnection experiments. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2008; 79:063505. [PMID: 18601406 DOI: 10.1063/1.2937193] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/26/2023]
Abstract
Experimental investigation of reconnection in magnetized plasmas relies on accurate characterization of the evolving magnetic fields. In experimental configurations where the plasma dynamics are reproducible, magnetic data can be collected in multiple discharges and combined to provide spatially resolved profiles of the plasma dynamics. However, in experiments on spontaneous magnetic reconnection recently undertaken at the Versatile Toroidal Facility at MIT, the reconnection process is not reproducible and all information on the plasma must be collected in a single discharge. This paper describes a newly developed magnetic flux array which directly measures the toroidal component of the magnetic vector potential, A(phi). From the measured A(phi), the magnetic field geometry, current density, and reconnection rate are readily obtained, facilitating studies of the three-dimensional dynamics of spontaneous magnetic reconnection. The novel design of the probe array allows for accurate characterization of profiles of A(phi) at multiple toroidal angles using a relatively small number of signal channels and with minimal disturbance of the plasma.
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Affiliation(s)
- A Kesich
- Massachusetts Institute of Technology, Plasma Science and Fusion Center, Cambridge, MA 02139, USA
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15
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Phan TD, Drake JF, Shay MA, Mozer FS, Eastwood JP. Evidence for an elongated (>60 ion skin depths) electron diffusion region during fast magnetic reconnection. PHYSICAL REVIEW LETTERS 2007; 99:255002. [PMID: 18233527 DOI: 10.1103/physrevlett.99.255002] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/09/2007] [Indexed: 05/25/2023]
Abstract
Observations of an extremely elongated electron diffusion region occurring during fast reconnection are presented. Cluster spacecraft in situ observations of an expanding reconnection exhaust reveal a broad current layer ( approximately 10 ion skin depths thick) supporting the reversal of the reconnecting magnetic field together with an intense current embedded at the center that is due to a super-Alfvénic electron outflow jet with transverse scale of approximately 9 electron skin depths. The electron jet extends at least 60 ion skin depths downstream from the X-line.
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Affiliation(s)
- T D Phan
- Space Sciences Laboratory, University of California, Berkeley, California 94720, USA
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16
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Zhang Y, Liu Z, Shen C, Duan S, He Z, Carr CM, Réme H. Double Star TC-1 observation of the earthward flowing plasmoids in the near magnetotail. CHINESE SCIENCE BULLETIN-CHINESE 2007. [DOI: 10.1007/s11434-007-0212-2] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
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17
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Cassak PA, Drake JF, Shay MA, Eckhardt B. Onset of fast magnetic reconnection. PHYSICAL REVIEW LETTERS 2007; 98:215001. [PMID: 17677781 DOI: 10.1103/physrevlett.98.215001] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/06/2007] [Indexed: 05/16/2023]
Abstract
We demonstrate the existence of a new steady-state magnetic reconnection configuration which lies at the boundary of the basins of attraction between the Sweet-Parker and Hall reconnection configurations. The solution is linearly unstable to small perturbations and its identification required a novel iterative numerical technique. The eigenmodes of the unstable solution are localized near the X line, suggesting that the onset of fast reconnection in a weakly collisional plasma is initiated locally at the X line as opposed to remotely at the boundaries.
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Affiliation(s)
- P A Cassak
- Department of Physics and Institute for Research in Electronics and Applied Physics, University of Maryland, College Park, Maryland 20742, USA
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18
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Inomoto M, Gerhardt SP, Yamada M, Ji H, Belova E, Kuritsyn A, Ren Y. Coupling between global geometry and the local hall effect leading to reconnection-layer symmetry breaking. PHYSICAL REVIEW LETTERS 2006; 97:135002. [PMID: 17026040 DOI: 10.1103/physrevlett.97.135002] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/29/2006] [Indexed: 05/12/2023]
Abstract
The coupling between the global reconnection geometry and the local microphysics, caused by the Hall effect, is studied during counterhelicity plasma merging in the magnetic reconnection experiment. The structure of the reconnection layer is significantly modified by reversing the sign of the toroidal fields, which affects the manifestation of the Hall effect in the collisionless regime. The local two-fluids physics changes the global boundary conditions, and this combination effect consequently provides different reconnection rates, magnetic field structure, and plasma flow patterns for two different counterhelicity merging cases in the collisionless regime.
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Affiliation(s)
- Michiaki Inomoto
- Center for Magnetic Self-Organization in Laboratory and Astrophysical Plasmas, Princeton Plasma Physics Laboratory, Princeton University, Princeton, NJ 08543, USA
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19
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Wygant JR, Cattell CA, Lysak R, Song Y, Dombeck J, McFadden J, Mozer FS, Carlson CW, Parks G, Lucek EA, Balogh A, Andre M, Reme H, Hesse M, Mouikis C. Cluster observations of an intense normal component of the electric field at a thin reconnecting current sheet in the tail and its role in the shock-like acceleration of the ion fluid into the separatrix region. ACTA ACUST UNITED AC 2005. [DOI: 10.1029/2004ja010708] [Citation(s) in RCA: 227] [Impact Index Per Article: 11.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Affiliation(s)
- J. R. Wygant
- School of Physics and Astronomy; University of Minnesota; Minneapolis Minnesota USA
| | - C. A. Cattell
- School of Physics and Astronomy; University of Minnesota; Minneapolis Minnesota USA
| | - R. Lysak
- School of Physics and Astronomy; University of Minnesota; Minneapolis Minnesota USA
| | - Y. Song
- School of Physics and Astronomy; University of Minnesota; Minneapolis Minnesota USA
| | - J. Dombeck
- School of Physics and Astronomy; University of Minnesota; Minneapolis Minnesota USA
| | - J. McFadden
- Space Sciences Laboratory; University of California; Berkeley California USA
| | - F. S. Mozer
- Space Sciences Laboratory; University of California; Berkeley California USA
| | - C. W. Carlson
- Space Sciences Laboratory; University of California; Berkeley California USA
| | - G. Parks
- Space Sciences Laboratory; University of California; Berkeley California USA
| | - E. A. Lucek
- Blackett Laboratory; Imperial College; London UK
| | - A. Balogh
- Blackett Laboratory; Imperial College; London UK
| | - M. Andre
- Swedish Institute of Space Physics; Uppsala Division; Uppsala Sweden
| | - H. Reme
- Centre d'Etude Spatiale des Rayonnements; Toulouse France
| | - M. Hesse
- NASA Goddard Space Flight Center; Greenbelt Maryland USA
| | - C. Mouikis
- University of New Hampshire; Durham New Hampshire USA
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Egedal J, Oieroset M, Fox W, Lin RP. In situ discovery of an electrostatic potential, trapping electrons and mediating fast reconnection in the Earth's magnetotail. PHYSICAL REVIEW LETTERS 2005; 94:025006. [PMID: 15698186 DOI: 10.1103/physrevlett.94.025006] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/11/2004] [Revised: 08/10/2004] [Indexed: 05/24/2023]
Abstract
Anisotropic electron phase space distributions, f, measured by the Wind spacecraft in a rare crossing of a diffusion region in Earth's far magnetotail (60 Earth radii), are analyzed. We use the measured f to probe the electrostatic and magnetic geometry of the diffusion region. For the first time, the presence of a strong electrostatic potential (1 kV) within the ion diffusion region is revealed. This potential has far reaching implications for the reconnection process; it accounts for the observed acceleration of the unmagnetized ions out of the reconnection region and it causes all thermal electrons be trapped electrostatically. The trapped electron motion implies that the thermal part of the electron distributions are symmetric around v( parallel)=0: f(v( parallel),v( perpendicular)) approximately f(-v( parallel),v( perpendicular)). It follows that the field aligned currents in the diffusion region are limited and fast magnetic reconnection is mediated.
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Affiliation(s)
- J Egedal
- Massachusetts Institute of Technology, Plasma Science Fusion Center, Cambridge, Massachusetts 02139, USA
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21
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Thompson SM. Dynamic Harris current sheet thickness from Cluster current density and plasma measurements. ACTA ACUST UNITED AC 2005. [DOI: 10.1029/2004ja010714] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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22
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Shiokawa K, Yago K, Yumoto K, Baishev DG, Solovyev SI, Rich FJ, Mende SB. Ground and satellite observations of substorm onset arcs. ACTA ACUST UNITED AC 2005. [DOI: 10.1029/2005ja011281] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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Vaivads A, Khotyaintsev Y, André M, Retinò A, Buchert SC, Rogers BN, Décréau P, Paschmann G, Phan TD. Structure of the magnetic reconnection diffusion region from four-spacecraft observations. PHYSICAL REVIEW LETTERS 2004; 93:105001. [PMID: 15447408 DOI: 10.1103/physrevlett.93.105001] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/22/2004] [Indexed: 05/24/2023]
Abstract
Magnetic reconnection leads to energy conversion in large volumes in space but is initiated in small diffusion regions. Because of the small sizes of the diffusion regions, their crossings by spacecraft are rare. We report four-spacecraft observations of a diffusion region encounter at the Earth's magnetopause that allow us to reliably distinguish spatial from temporal features. We find that the diffusion region is stable on ion time and length scales in agreement with numerical simulations. The electric field normal to the current sheet is balanced by the Hall term in the generalized Ohm's law, E(n) approximately jxB/ne.n, thus establishing that Hall physics is dominating inside the diffusion region. The reconnection rate is fast, approximately 0.1. We show that strong parallel currents flow along the separatrices; they are correlated with observations of high-frequency Langmuir/upper hybrid waves.
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Affiliation(s)
- A Vaivads
- Swedish Institute of Space Physics, Uppsala, Sweden
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ØIeroset M, Lin RP, Phan TD, Larson DE, Bale SD. Evidence for electron acceleration up to approximately 300 keV in the magnetic reconnection diffusion region of earth's magnetotail. PHYSICAL REVIEW LETTERS 2002; 89:195001. [PMID: 12443119 DOI: 10.1103/physrevlett.89.195001] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/28/2002] [Indexed: 05/24/2023]
Abstract
We report direct measurements of high-energy particles in a rare crossing of the diffusion region in Earth's magnetotail by the Wind spacecraft. The fluxes of energetic electrons up to approximately 300 keV peak near the center of the diffusion region and decrease monotonically away from this region. The diffusion region electron flux spectrum obeys a power law with an index of -3.8 above approximately 2 keV, and the electron angular distribution displays strong field-aligned bidirectional anisotropy at energies below approximately 2 keV, becoming isotropic above approximately 6 keV. These observations indicate significant electron acceleration inside the diffusion region. Ions show no such energization.
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Affiliation(s)
- M ØIeroset
- Space Sciences Laboratory, University of California, Berkeley, California 94720, USA
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Mozer FS, Bale SD, Phan TD. Evidence of diffusion regions at a subsolar magnetopause crossing. PHYSICAL REVIEW LETTERS 2002; 89:015002. [PMID: 12097047 DOI: 10.1103/physrevlett.89.015002] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/15/2002] [Indexed: 05/23/2023]
Abstract
On 1 April 2001, the Polar satellite crossed a subsolar magnetopause associated with antiparallel magnetic fields. Over a width approximately 6 magnetosheath ion skin depths (approximately 3 magnetospheric ion skin depths), perpendicular ion flows different from E x B/B(2) as well as Hall magnetic and electric field signatures were observed. At a smaller scale, the electron flow decoupled from the magnetic field near a deep minimum in the magnetic field strength. Separatrices were identified as boundaries of low frequency electric field turbulence associated with density minima and parallel electric fields. The reconnection rate was less than 2% of the asymptotic Alfvén speed.
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Affiliation(s)
- F S Mozer
- Space Sciences Laboratory, University of California, Berkeley, California 94720, USA
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27
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Hoshino M, Mukai T, Terasawa T, Shinohara I. Suprathermal electron acceleration in magnetic reconnection. ACTA ACUST UNITED AC 2001. [DOI: 10.1029/2001ja900052] [Citation(s) in RCA: 278] [Impact Index Per Article: 12.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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Oieroset M, Phan TD, Fujimoto M, Lin RP, Lepping RP. In situ detection of collisionless reconnection in the Earth's magnetotail. Nature 2001; 412:414-7. [PMID: 11473310 DOI: 10.1038/35086520] [Citation(s) in RCA: 411] [Impact Index Per Article: 17.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Magnetic reconnection is the process by which magnetic field lines of opposite polarity reconfigure to a lower-energy state, with the release of magnetic energy to the surroundings. Reconnection at the Earth's dayside magnetopause and in the magnetotail allows the solar wind into the magnetosphere. It begins in a small 'diffusion region', where a kink in the newly reconnected lines produces jets of plasma away from the region. Although plasma jets from reconnection have previously been reported, the physical processes that underlie jet formation have remained poorly understood because of the scarcity of in situ observations of the minuscule diffusion region. Theoretically, both resistive and collisionless processes can initiate reconnection, but which process dominates in the magnetosphere is still debated. Here we report the serendipitous encounter of the Wind spacecraft with an active reconnection diffusion region, in which are detected key processes predicted by models of collisionless reconnection. The data therefore demonstrate that collisionless reconnection occurs in the magnetotail.
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Affiliation(s)
- M Oieroset
- Space Sciences Laboratory, University of California, Berkeley, California 94720, USA.
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