Electric fields and currents in solar-terrestrial plasmas

Abstract

This article will review many ideas and concepts originally suggested by Alfvén (Space Sci Rev 7:1940, 1967) and Fälthammar (Rev Geophys 15: 457, 1977) on the important roles electric fields and currents play in solar-terrestrial plasmas. Much of our understanding of planetary and solar plasmas has come primarily from treating plasmas as fluids. Fluid theory has emphasized bulk parameters and frozen-in magnetic field. This article, however, will focus on electric field, currents, and particles. This approach will give us a much broader perspective about space and solar plasma dynamics. We review relevant observations, theories, and models that will help us understand the basic physics. Our discussion includes the heliospheric current sheet formed by the solar wind (SW). All of the planets are immersed in this current sheet, and magnetospheres are formed by the interaction of the current sheet with planetary magnetic fields. We discuss how the electric fields induced by the evolving current sheets can accelerate particles to high energies pertinent for auroras and solar flares. The magnetic polarity across the current sheets can reverse directions over a distance of a few Larmor radii. We review the orbit trajectories resulting from inclusion of a By component to the magnetic field and discuss how Speiser's calculations (Speiser in J Geophys Res 70:4219, 1965) are modified. We have applied both the Lorentz equation and Vlasov theory to boundary structures. We review how inhomogeneous magnetic field can produce parallel electric fields when electrons and ions mirror at different heights. Detailed observations of electrostatic waves and double layers discovered by instruments on S3-3 spacecraft are revisited. The Swift (J Geophys Res 80:2096, 1975) model of solitary waves and double layers reviewed by Goertz (Rev Geophys 17:418, 1979) is examined and discussed. We evaluate what is known and not known and the issues that still need to be resolved. Observations of electrostatic nonlinear structures in the SW are surprising. Although the sources of these structures are not known, these observations may be simply telling us that the solar corona, like Earth, may include mechanisms that can drive electric fields and currents along the magnetic field. Remarkable accomplishments have been made during the last 50 years but many problems still remain to be studied further and solved.