Kinetic simulations of electric field structure within magnetic island during magnetic reconnection and their applications to the satellite observations

摘要

Magnetic islands are considered to play a crucial role in collisionless magnetic reconnection. We use particle-in-cell simulations to investigate electric field E_z structure in the magnetic islands (including primary and secondary islands) with and without a guide field during magnetic reconnection. It is found that the electric field has multilayers in the primary island and a large bipolar structure in the secondary island in the absence of guide field. The electric field is provided by the Hall term (J × B)_z (mainly), the divergence of electron pressure tensor, and the convective term (V_i × B)_z in the outer and the inner region of primary island, while the electric field is much smaller (~0) in the middle and the core region of primary island due to the cancelation of the three terms. The single bipolar electric field is primarily provided by the Hall term in the secondary island. In the presence of a guide field, the electric field has multiple layers in the primary island (similar to zero guide field case) and the secondary island. However, there still exists one single large sharp bipolar structure of electric field in the central region of the secondary island. The differences of electric field in the primary and secondary islands are essentially due to the variations of the current J_y. These features can be used as the observational criteria to identify different types of magnetic islands in the magnetosphere using the data of future mission, such as the Magnetospheric Multiscale mission.