Evolution of thin current sheet with a southward interplanetary magnetic field studied by a three-dimensional electromagnetic particle code

This paper reports the spatial and temporal development of sheet current intensification in the near-Earth tail, using our three-dimensional global electromagnetic particle simulation with a southward turning interplanetary magnetic field (IMF) in it context of the substorm onset. As the solar wind with the southward IMF advances through the Earth, the near-Earth tail thins and the sheet current intensifies. The peak of the current density moves toward the Earth. Before its peak becomes maximum the reconnection takes place. The earthward flows are generated by the reconnection, which coincides with the earthward expansion of the intensified sheet current. Because of the pileup of the earthward plasma flows, the dawnward current is generated near the Earth. This dawnward current dissipates rapidly with the sheet current because of the opposite current direction, which coincides with the dipolarization in the near-Earth tail. This simulation study shows the sequence of the substorm dynamics in the near-Earth tail, which is similar to the features obtained by the multisatellite observations. The identification of the timing and mechanism of triggering substorm onset requires further studies in conjunction with observations.