Abstract
Magnetic reconnection processes in a kinked current sheet are investigated using threedimensional electromagnetic particleincell simulations in a large system where both the tearing and kink modes are able to be captured. The spatial resolution is efficiently enhanced using the adaptive mesh refinement and particle splittingcoalescence method. The kink mode scaled by the current sheet width such as is driven by the ions that are accelerated due to the reconnectionelectric field in the ionscale diffusion region. Although the kink mode deforms the current sheet structure drastically, the gross rate of reconnection is almost identical to the case without the kink mode and fast magnetic reconnection is achieved. The magnetic dissipation mechanism is, however, found very different between the cases with and without the kink mode. The kink mode broadens the current sheet width and reduces the electron flow velocity, so that the electron inertia resistivity is decreased. Nevertheless, anomalous dissipation through the electron thermalization compensates the decrease in the inertia resistivity so as to keep a high reconnection rate. This suggests that the electron dynamics in the electron diffusion region is automatically adjusted so as to generate sufficient dissipation for fast magnetic reconnection. The electron thermalization occurs effectively because the electron meandering scale along the current sheet is comparable to the wavelength of the kink mode. On the other hand, twodimensional simulations in the plane orthogonal to the magnetic field shows that in higher mass ratio cases with the electron thermalization is caused due to a hybridscale mode with wavelength intermediate between the ion and electron inertia lengths rather than the largescale kink mode with , because the electron meandering scale is shortened as the mass ratio increases.
The author is grateful to R. D. Sydora for useful and informative discussions. He acknowledges the hospitality of Department of Physics, University of Alberta, where he began the present work. Most of the calculations were performed by FUJITSU HPC2500 installed at the Information Technology Center, Nagoya University. This work has been partly supported by a collaborative research project at SolarTerrestrial Environment Laboratory, Nagoya University, and by a GrantinAid for Research Fellows of the Japan Society for the Promotion of Science (JSPS).
I. INTRODUCTION
II. SIMULATION MODEL
III. SIMULATION RESULTS IN 3D SYSTEM
A. Time evolution of the current sheet
B. Reconnection rate
C. Dissipation mechanism for fast magnetic reconnection
IV. SIMULATION RESULTS IN 2D SYSTEM
V. SUMMARY AND CONCLUSIONS
Key Topics
 Macroinstabilities
 91.0
 Magnetic reconnection
 38.0
 Diffusion
 29.0
 Electrical resistivity
 25.0
 Electric fields
 14.0
Figures
Results for Run2. (a) Time evolutions of the Fourier amplitude of averaged over the direction at for mode 0 (solid curve), mode 1 (dashed curve), and mode 6 (dotted curve). (b) 3D structure of the kinked current sheet at . Color contours represent the electron number density, and white curves are its isolines.
Results for Run2. (a) Time evolutions of the Fourier amplitude of averaged over the direction at for mode 0 (solid curve), mode 1 (dashed curve), and mode 6 (dotted curve). (b) 3D structure of the kinked current sheet at . Color contours represent the electron number density, and white curves are its isolines.
for Run2 averaged over the direction at . Solid curve denotes the result at , while dashed curve is the initial profile.
for Run2 averaged over the direction at . Solid curve denotes the result at , while dashed curve is the initial profile.
Schematic describing an integration region for calculating the global reconnection rate when magnetic reconnection takes place in a kinked current sheet. The global reconnection rate is obtained by integrating the electric field along the kinked line (thick solid curve).
Schematic describing an integration region for calculating the global reconnection rate when magnetic reconnection takes place in a kinked current sheet. The global reconnection rate is obtained by integrating the electric field along the kinked line (thick solid curve).
Time profiles of the global reconnection rate normalized by the upstream parameters for Run1 (dashed curve) and Run2 (solid curve).
Time profiles of the global reconnection rate normalized by the upstream parameters for Run1 (dashed curve) and Run2 (solid curve).
Electron flow velocity along the isoline of at and for Run1 (dashed curve) and Run2 (solid curve). The velocity and the position in the direction are averaged over the isoline.
Electron flow velocity along the isoline of at and for Run1 (dashed curve) and Run2 (solid curve). The velocity and the position in the direction are averaged over the isoline.
New coordinate (, ) system at and , in which axis is along the isoline of . White dashed curve represents the line where .
New coordinate (, ) system at and , in which axis is along the isoline of . White dashed curve represents the line where .
Generalized Ohm’s law in the coordinate system at for (a) Run1 and (b) Run2. Each term and position in the direction are averaged over the direction. is represented by black thick curve, by green curve, by blue curve, by pink curve, by light blue curve, by red curve, and sum of the righthand side of Eq. (4) by black light curve.
Generalized Ohm’s law in the coordinate system at for (a) Run1 and (b) Run2. Each term and position in the direction are averaged over the direction. is represented by black thick curve, by green curve, by blue curve, by pink curve, by light blue curve, by red curve, and sum of the righthand side of Eq. (4) by black light curve.
Electron pressure tensor term in the generalized Ohm’s law at for (a) Run1 and (b) Run2. Each component is averaged over the axis and is indicated by A, B, C, or D. The component A denotes , B , C , and D the sum of A, B, and C.
Electron pressure tensor term in the generalized Ohm’s law at for (a) Run1 and (b) Run2. Each component is averaged over the axis and is indicated by A, B, C, or D. The component A denotes , B , C , and D the sum of A, B, and C.
Profile along the axis through the line of at for Run1.
Profile along the axis through the line of at for Run1.
Electron distribution functions for (a), (b) Run1, and (c), (d) Run2. Positions are (a) , (b) , and [(c) and (d)] . The position for (c) and (d) is indicated by “” in Fig. 12(a).
Electron distribution functions for (a), (b) Run1, and (c), (d) Run2. Positions are (a) , (b) , and [(c) and (d)] . The position for (c) and (d) is indicated by “” in Fig. 12(a).
Time evolutions of the energy distribution in the space of the electrons which constitute a fluid element sampled in the upstream region, for (a) Run1 and (b) Run2. The electrons which have escaped from the plane through the line are removed from the fluid element. Black curve represents the bulk energy of the fluid element, while red curve denotes the thermal energy.
Time evolutions of the energy distribution in the space of the electrons which constitute a fluid element sampled in the upstream region, for (a) Run1 and (b) Run2. The electrons which have escaped from the plane through the line are removed from the fluid element. Black curve represents the bulk energy of the fluid element, while red curve denotes the thermal energy.
Results for Run2 at and . (a) , and (b) electron current density in the plane, , are superposed on the isolines of (black solid curve). Approximate line where is represented by thick black curve. Central region of the electron current sheet, where , is indicated by red (gray) shadow in (b).
Results for Run2 at and . (a) , and (b) electron current density in the plane, , are superposed on the isolines of (black solid curve). Approximate line where is represented by thick black curve. Central region of the electron current sheet, where , is indicated by red (gray) shadow in (b).
Profiles through the line at and of the term in the generalized Ohm’s law. Solid curve shows the case without highenergy electrons that satisfy or , and dashed curve is the case with all the electrons.
Profiles through the line at and of the term in the generalized Ohm’s law. Solid curve shows the case without highenergy electrons that satisfy or , and dashed curve is the case with all the electrons.
Time evolutions of the dissipation rate in the 2D simulations for the cases of (Run3), 100 (Run4), and 400 (Run5), which are indicated by arrows. The dissipation rate is normalized by the lobe parameters.
Time evolutions of the dissipation rate in the 2D simulations for the cases of (Run3), 100 (Run4), and 400 (Run5), which are indicated by arrows. The dissipation rate is normalized by the lobe parameters.
Results for Run5. (a) Snapshot at of the electron temperature in color contours, and isolines for in white curves. Electron temperature is normalized by the initial temperature. (b) Time evolutions of electron heating rate in red curve and in black curve, averaged over the entire system. (c) Time evolutions of the Fourier amplitude of averaged over the direction for mode 1 (solid curve) and mode 6 (dashed curve).
Results for Run5. (a) Snapshot at of the electron temperature in color contours, and isolines for in white curves. Electron temperature is normalized by the initial temperature. (b) Time evolutions of electron heating rate in red curve and in black curve, averaged over the entire system. (c) Time evolutions of the Fourier amplitude of averaged over the direction for mode 1 (solid curve) and mode 6 (dashed curve).
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