Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

We have clarified the. structure of asymmetric magnetic reconnection in detail as the result of the. spontaneous evolutionary process. The asymmetry is imposed as ratio k of the magnetic field strength in both sides of the initial current sheet (CS) in the isothermal equilibrium. The MHD simulation is carried out. by the HLLD code for the. long-term temporal evolution with very high spatial resolution. The resultant structure is drastically different from the symmetric case (e.g., the Petschek model) even for slight asymmetry k = 2.(1). The velocity distribution in the reconnection jet clearly shows a. two-layered structure, i.e., the high-speed sub-layer in which the flow is almost field aligned and the acceleration sub-layer. (2) Higher beta side (HBS) plasma is caught in a. lower beta side plasmoid. This suggests a new plasma mixing process in the reconnection events. (3) A new large strong fast shock in front of the plasmoid forms in the HBS. This can be a new particle acceleration site in the reconnection system. These critical properties that have. not been reported in previous works suggest that we contribute to a better and more detailed knowledge of the reconnection of the standard model for the symmetric magnetic reconnection system.

DOI： 10.3847/0004-637X/828/1/63

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER HEIDELBERG  

The 3D instability of spontaneous fast magnetic reconnection process is studied with magnetohydrodynamic simulations, where 2D model of the spontaneous fast magnetic reconnection process is destabilized in three dimensions. In this 3D instability, the spontaneous fast magnetic reconnection process is intermittently and randomly caused in 3D. In this paper, as a typical event study, a single 3D fast magnetic reconnection process often observed in the 3D instability is studied in detail. As a remarkable feature, it is reported that, when the 3D fast magnetic reconnection process starts, plasma inflows along the magnetic neutral line are observed, which are driven by plasma static pressure gradient along the neutral line. The plasma inflow speed reaches about 15 in the upstream field region. The unmagnetized inflow tends to prevent the 3D reconnection process; nevertheless, the 3D reconnection process is intermittently maintained. Such high-speed plasma inflows along the neutral line may be observed as dawn-dusk flows in space satellite observations of magnetotail's bursty bulk flows.

DOI： 10.1186/s40623-016-0462-9

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER HEIDELBERG  

Tailward flow in the near-Earth plasma sheet associated with a rebound of the earthward bursty bulk flow (BBF) is investigated using three-dimensional magnetohydrodynamics simulations of magnetic reconnection in the magnetotail on the basis of the spontaneous fast reconnection model. In order to investigate the properties of this tailward flow, virtual satellites are located at different positions in the plasma sheet within the simulation region, so that we can directly observe the temporal variations of plasma quantities in accordance with the growth and preceding the flow reversal associated with the magnetic reconnection. The time profile of the plasma flow velocity in the course of the BBF depends on the satellite position. Furthermore, the time profile of the magnetic field strength in the course of the reverse flow depends on the satellite position in the dawn-dusk direction. As a result of the rebound of the earthward flow, the accumulation of the plasma density and the plasma pressure is observed at any position in the plasma sheet during the interval between the BBF and the reverse flow.

DOI： 10.1186/s40623-014-0147-1

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST PHYSICS  

The 3D instability of the spontaneous fast magnetic reconnection process is studied with magnetohydrodynamics (MHD) simulations, where the 2D model of the spontaneous fast magnetic reconnection is destabilized in three dimension. As well known in many 2D numerical MHD studies, when a 1D current sheet is destabilized with the current-driven anomalous resistivity, the 2D Petschek type fast magnetic reconnection is established. This paper shows that the 2D Petschek type fast magnetic reconnection can be destabilized in three dimension by an initial resistive disturbance which includes a weak fluctuation in the sheet current direction, i.e., along the magnetic neutral line. The resulting 3D fast magnetic reconnection finally becomes intermittent and random through a 3D instability. In addition, it is also shown that the 3D instability is suppressed by the uniform resistivity. It suggests that the 3D instability is caused in the Petschek-type reconnection process which is characterized by a strongly localized magnetic diffusion region and the slow shock acceleration of the plasma jets and is suppressed in the Sweet-Parker type reconnection process. (C) 2013 AIP Publishing LLC.

DOI： 10.1063/1.4846857

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCI LTD  

Time profiles of some physical values in earthward fast flows in the plasma sheet are observed at three dimensionally different positions by employing virtual satellites located in the three-dimensional magnetohydrodynamic simulation domain, and these simulations are done on the basis of the spontaneous fast reconnection model. In the spontaneous fast reconnection evolution, the width of the flow channel is narrow in the dawn-dusk direction, and it does not spread until the plasma collides with the magnetic loop. The enhancements in B(z) and V(x) are larger at the center of the fast flow channel than those at its dawn and dusk edges, reflecting the differences in the reconnection rate in the diffusion region. The enhancement in V(x) is shorter near the plasma sheet boundary layer than that near the neutral sheet, reflecting the changes in the thickness of the flow channel. (C) 2011 COSPAR. Published by Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.asr.2011.03.025

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

Three-dimensional instability of the spontaneous fast magnetic reconnection is studied with magnetohydrodynamics (MHD) simulation, where the two-dimensional model of the spontaneous fast magnetic reconnection is destabilized in three dimensions. In two-dimensional models, every plasma condition is assumed to be uniform in the sheet current direction. In that case, it is well known that the two-dimensional fast magnetic reconnection can be caused by current-driven anomalous resistivity, when an initial resistive disturbance is locally put in a one-dimensional current sheet. In this paper, it is studied whether the two-dimensional fast magnetic reconnection can be destabilized or not when the initial resistive disturbance is three dimensional, i.e., that which has weak fluctuations in the sheet current direction. According to our study, the two-dimensional fast magnetic reconnection is developed to the three-dimensional intermittent fast magnetic reconnection which is strongly localized in the sheet current direction. The resulting fast magnetic reconnection repeats to randomly eject three-dimensional magnetic loops which are very similar to the intermittent downflows observed in solar flares. In fact, in some observations of solar flares, the current sheet seems to be approximately one dimensional, but the fast magnetic reconnection is strongly localized in the sheet current direction, i.e., fully three dimensional. In addition, the observed plasma downflows as snake-like curves. It is shown that those observed features are consistent with our numerical MHD study.

DOI： 10.1088/0004-637X/707/1/420

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST PHYSICS  

Three-dimensional instability of the spontaneous fast magnetic reconnection is studied with magnetohydrodynamic (MHD) simulation, where the two-dimensional model of the spontaneous fast magnetic reconnection is destabilized in three dimension. Generally, in two-dimensional magnetic reconnection models, every plasma condition is assumed to be uniform in the sheet current direction. In such two-dimensional MHD simulations, the current sheet destabilized by the initial resistive disturbance can be developed to fast magnetic reconnection by a current driven anomalous resistivity. In this paper, the initial resistive disturbance includes a small amount of fluctuations in the sheet current direction, i.e., along the magnetic neutral line. The other conditions are the same as that of previous two-dimensional MHD studies for fast magnetic reconnection. Accordingly, we may expect that approximately two-dimensional fast magnetic reconnection occurs in the MHD simulation. In fact, the fast magnetic reconnection activated on the first stage of the simulation is two dimensional. However, on the subsequent stages, it spontaneously becomes three dimensional and is strongly localized in the sheet current direction. The resulting three-dimensional fast magnetic reconnection intermittently ejects three-dimensional magnetic loops. Such intermittent ejections of the three-dimensional loops are similar to the intermittent downflows observed in the solar flares. The ejection of the three-dimensional loops seems to be random but, numerically and theoretically, it is shown that the aspect ratio of the ejected loops is limited under a criterion.

DOI： 10.1063/1.3095562

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：TERRA SCIENTIFIC PUBL CO  

Three-dimensional instability of spontaneous fast magnetic reconnection is studied using MHD (magneto-hydro-dynamic) Simulation. Previous two-dimensional MHD Studies have demonstrated that. if a current-driven anomalous resistivity is assumed, two-dimensional fast magnetic reconnection occurs and two-dimensional large- scale magnetic loops, i.e., plasmoids, are ejected from the reconnection re.-ion. In most two-dimensional MHD Studies, the Structure of the Current sheet is initially one-dimensinal. On the other hand, in recent space plasma observations, fully three-dimensional magnetic loops frequently appear even in the almost one-dimensional Current sheet. This suggests that the classical two-dimensional fast magnetic reconnection may be unstable to any three-dimensional perturbation, resulting in three-dimensional fast magnetic reconnection. In this paper, we show that a three-dimensional resistive perturbation destabilizes two-dimensional fast magnetic reconnection and results in three-dimensional fast magnetic reconnection. The resulting three-dimensional fast reconnection repeatedly ejects three-dimensional magnetic loops downstream. The obtained numerical results are similar to the pulsating downflows observed in solar flares. According to the Fourier analysis of the ejected magnetic loops, the time evolution of this three-dimensional instability is fully non-linear.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：TERRA SCIENTIFIC PUBL CO  

The earthward short-term (1-min. order) fast flow event (Flow Burst) and the long-term (10-min. order) fast flow event (Bursty Bulk Flow) observed in the near-Earth plasma sheet are examined using three dimensional MHD Simulations oil the basis of spontaneous fast reconnection model. It is well known that these fast flow events are closely related to the magnetic substorms. Oil the other hand, it is considered that these fast flow events are Caused by the magnetic reconnection in the near-Earth magnetotail. The time profiles of plasma quantities ill these events observed by in-situ satellites are quite different in each event. Above Flow Burst and Burst), Bulk Flow events are often examined separately due to the large difference in time scale. Ill this paper. these differences are interpreted by the three-dimensional position of satellite relative to the X-fine and the reconnection jet channel, and the simulation results are directly compared with the results of in-situ satellite observations using the virtual satellites located in simulation domain.

DOI： 10.1186/BF03352934

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：COPERNICUS PUBLICATIONS  

Three-dimensional configuration of earthward fast flow in the near-Earth plasma sheet is studied using three-dimensional magnetohydrodynamics (MHD) simulations on the basis of the spontaneous fast reconnection model. In this study, the sheared magnetic field in the plasma sheet is newly considered in order to investigate the effects of it to the earthward fast flow, and the results are discussed in comparison with no-shear simulations. The virtual probes located at different positions in our simulation domain in shear/no-shear cases could explain different behavior of fast flows in the real observations.

DOI： 10.5194/angeo-27-2297-2009

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：TERRA SCIENTIFIC PUBL CO  

The 3D spontaneous fast reconnection model is applied to well-known signatures of geomagnetic substorms and solar flares. First, it is applied to the traveling compression regions (TCRs) associated with plasmoids propagating down the tail plasma sheet, known its a definite signature of geomagnetic substorms. and the in-situ satellite observations can be precisely explained, both qualitatively and quantitatively. Then. it is demonstrated that the magnetospheric current wedge to link the fail Current,e drastically evolves through field-aligned currents to the auroral electrojet. It is also found that the well-known morphological features of two-ribbon flares call be explained by the fast reconnection model. In particular. the joule heating, associated with the flare Current wed-e. is shown to be important for the two-ribbon heating. Therefore, it is suggested that both solar flares and geomagnetic substorms result from the same physical mechanism, i.e., the fast reconnection mechanism.

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Blackwell Publishing Ltd  

The spontaneous fast reconnection model is applied to the earthward fast flow events observed in the near-Earth plasma sheet. Here, the earthward fast flow events include both of bursty bulk flow events and flow burst events. In order to apply it directly to actual observations, virtual probes are located in the plasma sheet region in the three-dimensional simulation domain so that we can directly observe the temporal variations of plasma quantities in accordance with the growth and proceeding of the fast reconnection. In this model, magnetic reconnection drastically evolves and Alfvénic fast plasma jet flows in the very restricted narrow channel, and a large-scale plasmoid is formed ahead of the fast plasma jet. The results of virtual observation of these evolutions are found to be in good agreement with actual satellite observations. At the same time, in the lobe region, travelling compression regions (TCRs) are observed in connection with the fast flow events. The temporal profiles of magnetic fields detected by the virtual probes are also in good agreement with actual satellite observations. It is concluded that the earthward fast flow events and earthward TCR events result from the fast reconnection mechanism. Copyright 2008 by the American Geophysical Union.

DOI： 10.1029/2007JA012707

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCI LTD  

Three dimensional structure of the fast convection flow in the plasma sheet is examined using magnetohydrodynamic (MHD) simulations on the basis of spontaneous fast reconnection model. The fast flow observed in the near-Earth magnetotail is one of the key phenomena in order to understand the causal relationship between magnetic substorm and magnetic reconnection. In this paper, we focus on this earthward fast flow in the near-Earth magnetotail. Our previous studies have shown that the fast reconnection produces the Alfvenic fast reconnection outflow and drastic magnetic field dipolarization in the finite extent. In this paper, the results of our simulations are compared with those of the in-situ observations in the geomagnetotail. They have consistent temporal profiles of the plasma quantities. It is suggested that the fast convection flows are caused by spontaneous fast reconnection. (C) 2007 COSPAR. Published by Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.asr.2007.02.021

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MHD study for the adiabatic expansion acceleration process associated with the spontaneous fast magnetic reconnection is reported. When the fast reconnection process steadily generates a plasmoid in the downstream, the adiabatic expansion acceleration region appears between the reconnection jet and plasmoid. It is pointed out that the appearance of the acceleration region is required to steadily keep the reconnection process. The reconnection jet and plasmoid is generally high beta but the plasma pressure in the acceleration region is extremely low, when the reconnection jet is supersonic. This feature may become a signature to detect where the Petschek reconnection is steadily caused in the current sheet of the geomagnetotail. (c) 2005 COSPAR. Published by Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.asr.2005.05.119

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On the basis of the spontaneous fast reconnection model, the underlying physical mechanism of magnetospheric current wedge evolution is studied by magnetohydrodynamic simulations. It is demonstrated that when a three-dimensional magnetic loop top is compressed by the fast reconnection jet, field-aligned currents are suddenly generated by the resulting sheared fields inside the loop
simultaneously, a large-scale current wedge evolves to link, through the field-aligned currents, the sheet current ahead of the magnetic loop to the current in the local loop footpoint of reconnected field lines. In accordance with the current-wedge evolution, the sheet current, which initially flows ahead of the loop top in the middle of the system, is abruptly bifurcated and turns its direction toward the local loop footpoint, where strong currents are concentrated and intensified. Therefore, once the channel for the current wedge is realized, effective energy dissipation occurs, through the channel, in the local region of the loop footpoint connected to the separatrix, which bounds the reconnected field lines and the ambient (prereconnection) field lines. © 2006 American Institute of Physics.

DOI： 10.1063/1.2359719

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE LTD  

The dynamics of large-scale magnetic loop in three dimensions is studied by MHD simulations. The spontaneous fast reconnection model is used in this study. Once a current-driven anomalous resistivity is ignited in a local region in a current sheet, the fast reconnection mechanism spontaneously evolves. As a result, large magnetic loop is developed, and very localized high pressure region appears outside of the magnetic loop. Near the region between magnetic loop and the high pressure region, very large vortex flow appears, and then, the high pressure region more and more localized due to this vortex. On the other hand, we suggest that the spatial size of initial disturbance to the direction of current is very important to evolve of three dimensional fast reconnection processes. (c) 2005 COSPAR. Published by Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.asr.2005.05.021

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Supersonic magnetic reconnection generating a plasmoid in the downstream region is studied in the Rankine Hugoniot analysis. It is theoretically shown that the pressure in the plasmoid is almost the same as the pressure in the supersonic reconnection jet. In addition, it is shown that the plasmoid propagation speed can be theoretically predicted from the plasmoid opening angle. The theoretically obtained pressure is consistent with the MHD simulation but the predicted plasmoid propagation speed resulted in slight over-estimation.

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Three dimensional dynamics of a magnetic loop is studied by magnetohydrodynamic simulations on the basis of the spontaneous fast reconnection model. In this model, petschek type fast reconnection is represented, so that a pair of slow shocks elongated from magnetic diffusion region and fast shock in front of magnetic loop top stand. It is interesting and important to study about three dimensional dynamics of these shock surfaces.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST PHYSICS  

The spontaneous fast reconnection model, is studied in a three-dimensional (3D) situation for different plasma parameter values. In any case, once a current-driven anomalous resistivity is ignited, magnetic reconnection explosively evolves as a nonlinear instability, and the 3D fast reconnection mechanism involving large-scale standing slow shocks is realized as an eventual solution on the nonlinear saturation phase. For the smaller plasma beta, the reconnection evolution is more drastic, and the resulting fast reconnection mechanism becomes more powerful. In the fast reconnection configuration, the central 3D diffusion region becomes unstable against resistive tearing and is bifurcated into a pair of diffusion regions, which move away from, each other. In the moving diffusion region, the locally enhanced anomalous resistivity is self-consistently sustained by the reconnection flow, and the slow shock stands between the 3D diffusion region and a large-scale 3D plasmoid. Since the plasmoid moves much more rapidly than the diffusion region, the 3D slow shock rapidly extends in the x direction in a finite extent in the z direction to occupy the overall system. In the wide range of plasma beta, the reconnection outflow jet u(x) attains the, Alfven velocity, measured in the ambient magnetic field region. Hence, the 3D fast reconnection mechanism established in the center of the system, which is consistent with the well-known 2D one, is sustained,steadily and extends outwards to drastically collapse the field system at large. (c) 2005 American Institute of Physics.

DOI： 10.1063/1.1883181

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：ELSEVIER SCIENCE BV  

The dynamics of large-scale magnetic loop in three dimensions is studied by MHD simulations. The spontaneous fast reconnection model is used in this study. In this model, the fast reconnection evolves by the positive feedback between microscopic anomalous resistivities and macroscopic reconnection flows. It is demonstrated that even in the general three-dimensional situation, once a current-driven anomalous resistivity is ignited in a local region in the current sheet, the fast reconnection mechanism spontaneously evolves explosively by such positive feedback. It is remarkable that a fast shock builds up ahead of the magnetic loop in a very limited extent, since the three dimension fast reconnection jet strongly converges toward the magnetic loop top as in the two-dimension case.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST PHYSICS  

The present paper studies the basic physics of the spontaneous fast reconnection model in a three-dimensional (3D) situation for different resistivity parameter values, where the threshold for occurrence of current-driven anomalous resistivity is allowed to increase with the thermal velocity (rootT), and the initial plasma density notably changes in space with the plasma pressure in the current sheet system. For any case, once the anomalous resistivity is ignited, the 3D fast reconnection mechanism explosively evolves as a nonlinear instability by the positive feedback between the anomalous resistivity and the reconnection flow, even if the threshold significantly increases with the thermal velocity; for the larger threshold values, the fast reconnection evolution becomes more drastic and the reconnection rate, finally attained on the nonlinear saturation phase, becomes larger. In the resulting 3D fast reconnection configuration, slow shocks stand and extend outwards in the finite extent; also, ahead of the fast reconnection jet, a large-scale 3D plasmoid swells and propagates in the central current sheet, and a vortex flow is formed near the plasmoid side boundary. In the wide range of parameter values, the basic physics of the 3D spontaneous fast reconnection evolution in the finite extent is found to be, qualitatively, consistent with the well-known two-dimensional one. (C) 2004 American Institute of Physics.

DOI： 10.1063/1.1677110

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Language：English   Publishing type：Research paper (international conference proceedings)  

The loop top shock structures and the associated plasma configurations around them are studied three dimensionally by computer simulations. For the spontaneous fast reconnection model, the quasi-steady and symmetric fast reconnection mechanism is set up without any significant dependence on plasma parameters. The super sonic reconnection jet between a pair of standing slow shocks collides with the loop and gives rise to a strong fast shock ahead of the loop top. These three dimensional basic features of magnetic loop development have been studied. The three dimensional shock structures, however, have not been understood because of the three-dimensional shocks were difficult to three dimensionally visualize it, In this paper, development of the loop top shock structures are investigated by effective visualization of them, The fast shock formed at loop top significantly depends on the separation of high-pressure region in magnetic loop and the associated vortex of plasma flow around the magnetic loop. © 2004 IEEE.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

The dawn-dusk magnetic field component (B,) in the plasmoid resulting of magnetic reconnections have been observed GEOTAIL satellite. We have studied the effects by B, component in the reconnection in geornagnetotail. This paper present the results of computer simulation about them. Our recent simulation apply the spontaneous fast reconnection model to the three-dimensional (3-D) plasmoid dynamics. Previous our original 3-D computational region (the first quadrant) is extended to the second quadrant and axis symmetry boundary conditions are used. Then, various initial values of dawn-dusk magnetic field component B, can be possibly assumed. As a result in all our simulation cases: (1) a large-scale plasmoid evolves, and (2) it propagates down to the geomagnetic tail, (3) slow shocks and finite amplitude intermediate waves simultaneously stand along the resulting plasmoid boundary layer. We also found that in the plasmoid where north-south magnetic field component (B,) changes its sign, B, also has a considerably big value, Which is consistent with the satellite observation result. We propose that the spontaneous fast reconnection mechanism could be most applicable to substorms. (C) 2003 COSPAR. Published by Elsevier Ltd. All rights reserved.

DOI： 10.1016/S0273-1177(03)00645-8

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

The spontaneous fast reconnection evolution is studied in asymmetric magnetic field configuration. In particular, it is investigated how shear flow influences in magnetosheath region to the propagation of plasmoid results from magnetic reconnection using two-dimensional magnetohydrodynamic simulations. According to the fast reconnection development, the resulting large-scale plasmoids swell and propagate. Once the plasmoid fully develops, the propagation speed becomes almost constant in both the symmetric and asymmetric magnetic field configuration. An asymmetric plasmoid swells predominantly in the region of a weaker magnetic field and propagates along the field lines. The associated shock structure standing at the plasma boundary is the ordinary slow shock irrespective of the intensity of shear flow. However, velocity of plasmoid is proportional to shear flow velocity. (C) 2003 COSPAR. Published by Elsevier Ltd. All rights reserved.

DOI： 10.1016/S0273-1177(03)00644-6

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST PHYSICS  

Three-dimensional (3D) dynamics of a large-scale magnetic loop is studied by precise magnetohydrodynamic simulations on the basis of the spontaneous fast reconnection model. Once a (current-driven) anomalous resistivity is ignited, the fast reconnection mechanism drastically evolves by the positive feedback between the (3D) global reconnection flow and the anomalous resistivity; on the nonlinear saturation phase, the global reconnection flow has grown so that the reconnection (diffusion) region shrinks to a small extent, and the fast reconnection mechanism involving a pair of standing slow shocks is established in the finite extent. When the 3D plasmoid, formed ahead of the fast reconnection jet, collides with the mirror plane boundary, the reconnected field lines are piled up, leading to formation of a large-scale 3D magnetic loop. Since the resulting 3D fast reconnection jet becomes supersonic, a definite fast shock builds up at the interface between the magnetic loop top and the fast reconnection jet. The 3D fast reconnection jet is limited in a narrow channel between the pair of slow shocks, so that the resulting fast shock is also limited to a small extent ahead of the magnetic loop top. On the other hand, for the uniform resistivity model the 3D fast reconnection mechanism cannot be realized without any vital positive feedback between the reconnection flow and the local magnetic diffusion; hence, such an effective resistivity that can be self-consistently enhanced locally at the X reconnection point by the global reconnection flow is essential for the fast reconnection mechanism to be realized in actual systems. (C) 2003 American Institute of Physics.

DOI： 10.1063/1.1536613

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

Flux transfer events (FTEs) observed at the dayside magnetopause is studied on the basis of the spontaneous fast reconnection model. If an X neutral point is not located at the sub-solar point, the flux transfer event may be significantly influenced by solar wind. With this in mind, we investigate the effects of solar wind on the flux transfer event by 2-dimensional MHD simulations. Unlike the previous simulations with the locally fixed resistivity model, the present study assumes an anomalous resistivity to be self-consistently determined by the reconnection flow, so that the resulting X point is allowed to move freely. It is demonstrated that at the early stage a single X point appears and moves in the direction of solar wind. Then, a new X point suddenly appears because of the secondary tearing, and a rather small magnetic island appears. The reconnection rate at the new X point is weaker than that at the original X point, so that the magnetic island moves in the direction of the solar-wind upstream. (C) 2002 COSPAR. Published by Elsevier Science Ltd. All rights reserved.

DOI： 10.1016/S0273-1177(02)00031-5

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST PHYSICS  

The spontaneous fast reconnection evolution is studied in a long current sheet system in various physical situations, where the threshold of current-driven anomalous resistivity is assumed to increase with the thermal velocity. If the initial threshold V-C0 is sufficiently large in a low-beta plasma, the fast reconnection mechanism can fully be set up; on the other hand, if V-C0 is so small that the anomalous resistivity can easily occur in the usual circumstances, the resulting diffusion region notably lengthens so that the reconnection process becomes much less effective. Also, the fast reconnection evolution is strongly influenced by plasma beta in the ambient magnetic field region, and an essential condition for the fast reconnection mechanism to evolve explosively is that the plasma beta is sufficiently small. In fact, only in a low-beta plasma does the magnetic tension force involved play the dominant role in the overall system dynamics and in the drastic magnetic energy release. It is also demonstrated that the fast reconnection evolution does not depend on the detailed functional form of the (current-driven) anomalous resistivity model. This is because the positive feedback between the anomalous resistivity and the reconnection flow effectively works so long as an anomalous resistivity is assumed to increase with the relative electron-ion drift velocity. (C) 2001 American Institute of Physics.

DOI： 10.1063/1.1360212

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON PRESS LTD  

We have investigated the relationship between solar wind speeds and the energetic proton intensity associated with corotating interaction regions (CIR) observed at 1 AU during 1973 - 1995 using NSSDC Data. The speed-difference between the high-speed solar wind and the slow-speed solar wind, which forms CIR at outer heliosphere, shows a good correlation with the peak intensity of 1 - 2 MeV protons during the solar quiet periods. The speed-difference is probably related to the shock strength of the reverse shock of the CIR formed beyond - 1 AU. We have also found the solar activity dependence of the correlation between these quantities in CIR events during the period between 1973 and 1995. The intensity of CIR particles during the solar active periods is higher than that during the quiet periods, suggesting that the density of seed particles in CIR events during the solar active periods is larger than that during the solar quiet period. (C) 2000 COSPAR. Published by Elsevier Science Ltd.

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Language：Japanese   Publisher：The Physical Society of Japan  

DOI： 10.11316/jpsgaiyo.54.1.1.0_73_4

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON PRESS LTD  

Long-term decrease events in the intensity of galactic cosmic rays have been investigated using solar wind parameters. We investigated distinct long-term decreases in 1993/94 near the solar minimum phase. In this period, the corotating interaction regions were observed over half a year. Recurrent increases of the solar wind speed were observed during this time period, forming corotating interaction regions. Simultaneously recurrent energetic proton events and recurrent decrease of galactic cosmic rays are measured. The baseline counts of neutron monitors was well anti-correlated with the peak speed of solar wind. It is suggested that long-lasting enhancements of solar wind velocity or corotating interaction regions formed by them can produce, the long-term decrease in the galactic cosmic ray intensity. (C)1999 COSPAR. Published by Elsevier Science Ltd.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON PRESS LTD  

The energy spectra (40 to 300 MeV/n) of galactic cosmic ray particles (C, N, O, Ne, Mg, Si, and Fe) observed by the HEP-HI silicon detector telescope onboard the GEOTAIL satellite were investigated over the period from January 1993 to May 1996, from the viewpoint of solar modulation. From the GEOTAIL data and those of relativistic heavy particles observed by HEAO-3, the modulation potential phi was obtained by using a solution of the Fokker-Plank equation with the "force-field" approximation. In the equation the diffusion coefficient was used as adjustable parameter, under the assumptions of a fixed velocity of solar wind (400 km/sec) and the radius of the heliosphere of 50 AU. The time variation of the modulation potential thus obtained is compared with that obtained from the CLIMAX neutron monitor. A reasonable correlation between both time variations is found when five months delay is applied to the results obtained by the HEP-HI telescope. (C) 1999 COSPAR. Published by Elsevier Science Ltd.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PHYSICAL SOC JAPAN  

A series of corotating energetic helium events with 3-5 MeV/n has been observed by the HEP telescopes onboard the GEOTAIL satellite at 1AU from October 1993 to August 1994. We have examined the relationship between solar wind (SW) speeds observed at 1AU and the intensity of He in the series of the corotating interaction region (CIR) events. The speed difference of the high-speed SW from slow-speed SW; which forms a CIR in the outer heliosphere, shows a reasonable correlation with the peak intensity of He at 3-5 MeV/n. The speed difference of those SWs is considered to be related to the shock strength which develops in a CIR at a distance from the Sun. Such a correlation between energetic ions associated with CIRs and SW speed has not been shown so far for the events during the period of 1978-1986. We have also investigated the dependence of the relation between the CIR ion events and the SW speeds during the period between 1978 and 1995 which corresponds to the high solar active phase of Solar Cycle 22. There is a good correlation between the SW speed and the peak intensity of CIR energetic ions in the quiet phase of solar activity, but not in the active phase.

DOI： 10.1143/JPSJ.67.3991

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Language：Japanese   Publisher：The Physical Society of Japan  

DOI： 10.11316/jpsgaiyo.53.1.1.0_82_4

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：UNIV CHICAGO PRESS  

The Geotail high-energy particle instruments have observed cosmic-ray particles in the energy range from 3 MeV n(-1) to 150 MeV n(-1) at 1 AU during the period 1992 September-1995 August. A remarkable enhancement of anomalous cosmic-ray (ACR) N, O, Ne, and C is observed during the period. A measurable enhancement of the sulfur flux below about 20 MeV n(-1) was observed. This is the first evidence showing the existence of sulfur in the anomalous component. The flux increase of anomalous sulfur, with a first ionization potential (FIP) of 10.4 eV, is smaller than that of ACR carbon with an FIP of 11.3 eV and much smaller than those of high-FIP elements, which suggests that the fractions of neutral carbon and sulfur atoms are significantly low in the very local interstellar medium.

DOI： 10.1086/310533

Web of Science

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Language：Japanese   Publisher：The Physical Society of Japan  

DOI： 10.11316/jpsgaiyo.52.2.1.0_80_3

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON PRESS LTD  

The composition and energy spectra of anomalous cosmic-rays (ACRs) in the energies 6 - 200 MeV/n have been measured during the period from September 1992 to August 1995 using the High Energy Particle instrument onboard the GEOTAIL satellite orbiting at 1 AU. A remarkable enhancement of ACR N, O, Ne and Ar is observed during the period. A flux enhancement of anomalous argon at 1 AU is confirmed by the GEOTAIL satellite. The first possible evidence for the emergence of a measurable sulfur component in ACR below about 20 MeV/n is found, The flux increase of anomalous sulfur with 10.4 eV FIP is smaller than that of ACR carbon with 11.3 eV FIP, and much smaller than those of high FIP elements, which suggests that the fraction of neutral carbon and sulfur atoms is significantly lower in the very local interstellar medium. (C) 1997 COSPAR.

DOI： 10.1016/S0273-1177(96)00152-4

Web of Science

Scopus

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Language：Japanese   Publisher：The Physical Society of Japan  

DOI： 10.11316/jpsgaiyo.52.1.1.0_93_2

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Publishing type：Part of collection (book)   Publisher：American Geophysical Union  

DOI： 10.1029/gm097p0255

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Language：Japanese   Publisher：The Physical Society of Japan  

DOI： 10.11316/jpsgaiyoj.1996.1.0_173_2

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Language：English   Publisher：TERRA SCIENTIFIC PUBL CO  

Interplanetary ions in a few MeV/n energies were observed by the GEOTAIL spacecraft at 1 AU during the period from December 1993 to April 1994. The measurements were performed with the HEP-particle telescopes on board the GEOTAIL. We have examined the correlation between the interplanetary ion events and cosmic ray modulation. It is found that the variation of counting rates of neutron monitor is well correlated with the flux variation of low energy ions. The corotating interaction regions formed in the interplanetary space significantly affect the intensities not only of low energy galactic cosmic rays (GCRs) but also of high energy GCRs. It implies that corotating streams cause the decrease of GCR flux because they act as barriers that impede the flows of GCRs toward the Sun.

DOI： 10.5636/jgg.47.1333

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Language：Japanese   Publisher：Ehime University  

CiNii Books

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J-GLOBAL

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J-GLOBAL

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Language：Japanese   Publisher：The Physical Society of Japan (JPS)  

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The First Observation of Sulfur in Anomalous Cosmic Rays by the GEOTAIL and the WIND Spacecrafts(共著) T.Takashima, T.Doke, T.Hayashi, J.Kikuchi, M.Kobayashi, H.Shirai, N.Takehana, M.Ehara, Y.Yamada, S.Yanagita, N.Hasebe, T.Kashiwagi,C.Kato, K.Munakata, T.Kohno, H.Murakami, A.Nakamoto,T.Yanagimachi

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The Geotail high-energy particle instruments have observed cosmic-ray particles in the energy range from 3 MeV n -1 to 150 MeV n -1 at 1 AU during the period 1992 September-1995 August. A remarkable enhancement of anomalous cosmic-ray (ACR) N, O, Ne, and C is observed during the period. A measurable enhancement of the sulfur flux below about 20 MeV n -1 was observed. This is the first evidence showing the existence of sulfur in the anomalous component. The flux increase of anomalous sulfur, with a first ionization potential (FIP) of 10.4 eV, is smaller than that of ACR carbon with an FIP of 11.3 eV and much smaller than those of high-FIP elements, which suggests that the fractions of neutral carbon and sulfur atoms are significantly low in the very local interstellar medium. © 1997. The American Astronomical Society. All rights reserved.

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The First Observation of Sulfur in Anomalous Cosmic Rays by the GEOTAIL and the WIND Spacecrafts(jointly worked) T.Takashima, T.Doke, T.Hayashi, J.Kikuchi, M.Kobayashi, H.Shirai, N.Takehana, M.Ehara, Y.Yamada, S.Yanagita, N.Hasebe, T.Kashiwagi,C.Kato, K.Munakata, T.Kohno, H.Murakami, A.Nakamoto,T.Yanagimachi

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The loop top shock structures and the associated plasma configurations around them are studied three dimensionally by computer simulations. For the spontaneous fast reconnection model, the quasi-steady and symmetric fast reconnection mechanism is set up without any significant dependence on plasma parameters. The super sonic reconnection jet between a pair of standing slow shocks collides with the loop and gives rise to a strong fast shock ahead of the loop top. These three dimensional basic features of magnetic loop development have been studied. The three dimensional shock structures, however, have not been understood because of the three-dimensional shocks were difficult to three dimensionally visualize it, In this paper, development of the loop top shock structures are investigated by effective visualization of them, The fast shock formed at loop top significantly depends on the separation of high-pressure region in magnetic loop and the associated vortex of plasma flow around the magnetic loop. © 2004 IEEE.

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The dynamics of large-scale magnetic loop in three dimensions is studied by MHD simulations. The spontaneous fast reconnection model is used in this study. In this model, the fast reconnection evolves by the positive feedback between microscopic anomalous resistivities and macroscopic reconnection flows. It is demonstrated that even in the general three-dimensional situation, once a current-driven anomalous resistivity is ignited in a local region in the current sheet, the fast reconnection mechanism spontaneously evolves explosively by such positive feedback. It is remarkable that a fast shock builds up ahead of the magnetic loop in a very limited extent, since the three dimension fast reconnection jet strongly converges toward the magnetic loop top as in the two-dimension case. © 2005 Elsevier B.V. All rights reserved.

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