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Ann. Geophys., 24, 1137-1143, 2006
www.ann-geophys.net/24/1137/2006/
© European Geosciences Union 2006
Time development of electric fields and currents in space plasmas
A. T. Y. Lui
The Johns Hopkins University, Applied Physics Laboratory, Laurel, MD 20723-6099, USA
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.
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