Heliophysics Science Division
TYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"> Ken Nishikawa - Abstract

Global Particle Simulation Study of Substorm Onset and Particle Acceleration


Dr. Ken Nishikawa
Department of Physics and Astronomy
Rutgers University

This talk reports the spatial and temporal development of Bursty Bulk Flows (BBFs) created by the reconnection as well as current disruptions (CDs) in the near-Earth tail using our 3-D global EM particle simulation with a southward turning IMF in the context of the substorm onset. Recently, observations show that BBFs are often accompanied by current disruptions for triggering substorms. We have examined the dynamics of BBFs and CDs in order to understand the timing and triggering mechanism of substorms. As the solar wind with the southward IMF advances over the Earth, the near-Earth tail thins and the sheet current intensifies. Before the peak of the current density becomes maximum, the reconnection takes place, which ejects particles from the reconnection region. Because of the earthward flows the peak of the current density moves toward the Earth. The characteristics of the earthward flows depend on the ions and electrons. Electrons flow back into the inflow region (the center of reconnection region), which provides current closure. Therefore the structure of electron flows near the reconnection region is rather complicated. In contrast, the ion earthward flows are generated far from the reconnection region. These earthward flows pile up near the Earth. The ions mainly drift toward the duskside. The electrons are diverted toward the dawnside. Due to the pile-up, 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. At this time the wedge current may be created in our simulation model. 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. The rationale why global particle simulation is necessary in the future will be discussed.