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In this paper, by taking advantage of a two-dimensional particle-in-cell simulation model, we study the structure of the out-of-plane magnetic field (Hall magnetic field) during asymmetric magnetic reconnection without a guide field, and the associated in-plane current system is also analyzed. The evolution of asymmetric reconnection has two stages. At the first stage, the electrons move toward the X line along the separatrix in the magnetosheath side, and depart from the X line along the separatrix in the magnetosphere side. Another electron flow toward the X line exists above the separatrix in the magnetosphere side. The resulted in-plane current system, which is mainly determined by electron dynamics, generates the quadrupolar structure of the Hall magnetic field, where the two quadrants in the magnetosheath side are much stronger than those in the magnetosphere side. At the second stage, besides these electron flows, an additional electron flow away from the X line is formed along the magnetic field below the separatrix in the magnetosheath side. A hexapolar structure of the Hall magnetic field is then generated by such a current system. [ABSTRACT FROM AUTHOR]

A test particle code is employed to explore the dynamics of charged particles and perpendicular diffusion in turbulent magnetic field, where a three-dimensional (3D) isotropic turbulence model is used in this paper. The obtained perpendicular diffusion at different particle energies is compared with that of the nonlinear guiding center (NLGC) theory. It is found that the NLGC theory is consistent with test particle simulations when the particle energies are small. However, the difference between the NLGC theory and test particle simulations tends to increase when the particle energy is sufficiently large, and the threshold is related to the turbulence bend-over length. In the NLGC theory, the gyrocenter of a charged particle is assumed to follow the magnetic field line. Therefore, when the particle has sufficiently large energy, its gyroradius will be larger than the turbulence bend-over length. Then the particle can cross the magnetic field lines, and the difference between the test particle simulations and NLGC theory occurs. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) particle-in-cell simulations are performed to investigate the structures of the out-of-plane magnetic field in magnetic island, which is produced during anti-parallel collisionless magnetic reconnection. Regular structures with alternate positive and negative values of the out-of-plane magnetic field along the x direction are formed in magnetic island. The generation mechanism of such structures is also proposed in this paper, which is due to the Weibel instability excited by the temperature anisotropy in magnetic island. [ABSTRACT FROM AUTHOR]