Roles of Plasma Sheet Flow, Plasma Sheet Dissipation and the M-I Coupling in Reproducing the Substorm With the Global Simulation

Abstract

The substorm is reproduced from the REPPU (REProduce Plasma Universe) global simulation. A quasi-steady state is generated under the northward interplanetary magnetic field (IMF), and then the IMF is turned southward to generate the substorm. In the initial state, significant earthward plasma sheet flow is maintained assuming dissipation at the distant tail. Such plasma sheets are not only confined but also convective, where the M-I (magnetosphere-ionosphere) coupling and region-2 field-aligned current (FAC) play a partial role in confinement. Ionospheric convection accelerates the thinning during the growth phase and dissipation in the distant tail makes the near-earth neutral line (NENL) retreat to the mid-tail. 9 min before the onset, the plasmoid, the NENL, and the flux rope are generated from far to near earth. When the dipolarization front (DF) that starts from the mid-tail NENL reaches the near-earth tail, the onset FAC appears through the formation of the near-earth dynamo, followed by the poleward expansion. These processes are projected only to a narrow latitudinal region of the ionosphere. The expansion phase develops appropriately by large dissipation assumed at X points to approximate kinetic effects. Formations of the NENL and the flux rope proceed under a mechanically balanced structure in the plasma sheet, which is realized upon the global conflict among ionospheric convection, magnetospheric flow, magnetic structure and dissipation distribution. Global magnetohydrodynamic (MHD) simulation enables to reproduce such properly balanced structures. Finally, earthward flow from the NENL overwhelms tailward flow from the flux rope, and eventually the whole feature appears the outside-in.