Dynamics of the Magnetotail Plasma Sheet Current

Abstract

Magnetospheric plasma can be investigated as a continuum by adopting magnetic field B and plasma flow u as primary parameters in the Bu paradigm or as a collection of individual particles by adopting electric field E and electrical current j as primary parameters in the Ej paradigm. It is pointed out that each paradigm has its merits and limitations. This viewpoint is illustrated further by examining several topics in magnetospheric research. The magnetic flux transport in substorm dipolarization is examined with the Ej paradigm to show why the Bu paradigm may be inappropriate in some cases due to the violation of the frozen-in condition for the validity of the Bu paradigm. There is no guarantee that large-scale plasma dynamics can always be treated accurately by the Bu paradigm. The disturbance revealed in the current disruption (CD) phenomenon has unique characteristics that can be more readily understood with the Ej paradigm. In a case study, the power dissipation in CD is evaluated to about an order of magnitude higher than that in the electron diffusion region associated with magnetic reconnection (MR). Two prominent plasma instabilities, namely tearing instability (TI) and cross-field current instability (CCI), are discussed and their relevance to substorm onset is evaluated. The mating instability developed conceptually is also briefly discussed. The development of azimuthal auroral beads (ABs) on auroral arcs formed prior to substorm onset is analyzed to show that CCI can predict well their wavelength, growth rate, and period simultaneously. In contrast, the observed azimuthal structures in ABs are inconsistent with TI that produces only meridian structures in the ionosphere. Overall, the physical insights gained in the Ej paradigm are helpful in achieving a deep understanding of several magnetospheric phenomena.