Abstract
Abstract. Two different approaches, referred to as Bu and Ej, can be used to examine the time development of electric fields and currents in space plasmas based on the fundamental laws of physics. From the Bu approach, the required equation involves the generalized Ohm's law with some simplifying assumptions. From the Ej approach, the required equation can be derived from the equation of particle motion, coupled self-consistently with Maxwell's equation, and the definition of electric current density. Recently, some strong statements against the Ej approach have been made. In this paper, we evaluate these statements by discussing (1) some limitations of the Bu approach in solving the time development of electric fields and currents, (2) the procedure in calculating self-consistently the time development of the electric current in space plasmas without taking the curl of the magnetic field in some cases, and (3) the dependency of the time development of magnetic field on electric current. It is concluded that the Ej approach can be useful to understand some magnetospheric problems. In particular, statements about the change of electric current are valid theoretical explanations of change in magnetic field during substorms.
Highlights
Some space plasma researchers are keenly aware of a seemingly everlasting controversy on the “correct” approach in developing theoretical understanding of magnetospheric phenomena
Several strong criticisms have been made against the Ej approach in addressing the time development of electric fields and currents in plasmas
We show the approximations used in reaching these criticisms are not applicable to the theory for current disruption in substorms
Summary
The time development of electric current is examined by Vasyliunas (2005). The main points stated there are: (1) on time scales longer than the electron plasma period, j should only be determined by curl of B; (2) on similar time scales, E should only be determined by the generalized Ohm’s law; and (3) substorm theory of current disruption is merely a description of change in magnetic field and not an explanation. We examine the logic behind these statements and identify their problems. We provide counter examples to invalidate these assertions. The SI unit will be used throughout this paper
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