Formation of magnetospheric plasma population regimes coupled with the dynamo process in the convection system

Abstract

Based on the magnetosphere-ionosphere (M-I) coupling scheme, convection as a compound system is considered including the generation of plasma population regimes in the magnetosphere. In these considerations, primary elements that must be set to a selfconsistent configuration are convection flows in the magnetosphere and the ionosphere, field-aligned current (FAC) systems, ionospheric currents, energy conversion processes, and plasma population regimes. The convection in the M-I coupling system is inextricably associated with the FACs. In the present results, the region-1 and region-2 FACs are driven by ∇P current inside the magnetosphere through plasma internal energy accumulated in the cusp and plasma sheet, respectively. In this process, mechanisms to drive the region-1 and region-2 FACs are the same two-step process; tangential Maxwell stress on the magnetopause pumps up plasma internal energy inside the magnetosphere, then plasma internal energy drives the FACs. This dynamo can be driven by a steady convection flow which is suitable to project down to the low-β regions. Thus from the magnetohydrodynamic (MHD) force balance controlling the convection, plasma population regimes appear through a requirement to form dynamo in the magnetosphere, showing that plasma population regimes are indispensable to fulfill the self-consistency in the convection system. In the model that the convection is driven directly by the linetying current, the shoulder of the magnetosphere behind the cusp, where the line-tying current is mixed with the pure Chapman-Ferraro current connected to dayside, constructs the dynamo (JE < 0) for the region-1 FAC. In the present model with negative IMF Bz, on the contrary, the Chapman-Ferraro current in this area is not directly connected with the region-1 FAC but connected with the neutral sheet current in the dayside merging region to increase plasma internal energy (JE > 0) around the cusp. Similarly, tail theta current system acts to increase plasma internal energy in the plasma sheet through the convection. The magnetospheric model derived from this consideration enables a continuous switch over from the confinement state of geomagnetic field in the ChapmanFerraro model to the convection of Dungey model for nonzero IMF Bz. In the present convection model, nearly force-free open field lines are extending from the polar cap into the lobes. Based on the convection model proposed in this paper, a suggestion is given for the substorm models in the next decade that they must develop from a modular model to a globally self-consistent model. Copyright 2003 by the American Geophysical Union.