Development of the Substorm as a Manifestation of Convection Transient

Abstract

We reproduced the substorm by global simulation and analyzed the development of convection, shear, the dynamo, and the field-aligned current (FAC) at the final stage of the growth phase. From these investigations, we show that the substorm is a manifestation of reconfiguration in global flow dynamics. Ionospheric convection can be understood from two aspects. One understanding is as the potential field generated by the FAC, and the other is as the projection of magnetospheric convection. In order for the two to coincide, the FAC must be transmitted together with the motion. As a consequence, the resulting convection must be continuous from the magnetosphere to the ionosphere. We see this connection from the drawing of shear to recognize that the substorm is the projection process of transient convection. In the growth phase, convective shear that causes the quiet arc and the Harang reversal (HR) occurs on the open/closed boundary along the surface of the plasma sheet with a continuous flow structure from the magnetosphere to the ionosphere. The onset starts from a more local flow that is induced by the near-earth neutral line (NENL). A narrow shear commences from the NENL in the mid-tail and extends to the ionosphere to replace growth phase shear. Along a closed magnetic field line connected to the NENL, direct penetration flow, squeezing flow, the near-earth dynamo, release of the HR, and the onset FAC occur successively and consequently cause the ground onset. Such onset mechanism is quite different from the model adopting the current wedge.