Out-of-plane electron currents in magnetic islands formed during collisionless magnetic reconnection

Secondary islands are considered to play a crucial role in collisionless magnetic reconnection. Based on 2-D particle-in-cell simulations, we investigate the characteristics of the out-of-plane electron currents in magnetic islands formed during collisionless magnetic reconnection with an initial guide field. In a primary island (formed simultaneously with the appearance of the X lines), due to the acceleration of the trapped electrons, the direction of the formed out-of-plane electron current is reverse to the original one. In the secondary island (formed in the vicinity of the X-line), the out-of-plane electron current is generated due to the accelerated electrons by the reconnection electric field in the vicinity of the X line. In such a way, the direction of the out-of-plane electron current in a secondary island is found to be opposite to that in a primary island. Such characteristics are found to be related to the evolution of the magnetic islands and then electron dynamics in the islands, which are proposed in this paper to be a possible criterion to identify a secondary island formed during collisionless magnetic reconnection, especially in the magnetotail. Key Points a criterion to identify a secondatry island is proposed The j-ey in a secondary island is opposite to that in a primary island The generation of J-ey in islands is proposed.