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Astron. Astrophys. 321, 945-959 (1997)


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Solar wind velocity jumps across tangential discontinuities: Ulysses observations and kinetic interpretation

J. De Keyser 1, M. Roth 1, B.T. Tsurutani 2, C.M. Ho 2 and J.L. Phillips 3

1 Belgian Institute for Space Aeronomy, Ringlaan 3, B-1180 Brussels, Belgium
2 Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USA
3 Los Alamos National Laboratory, Los Alamos, NM 87545, USA

Received 17 May 1996 / Accepted 24 October 1996

Abstract

Some tangential discontinuities (TDs) observed by the Ulysses spacecraft interface solar wind regions that differ only in their bulk velocity and magnetic field orientation; composition, density, temperature and magnetic field intensity are essentially the same in both regions. The relation between the plasma velocity jump across the TD and the magnetic field is investigated through the analysis and simulation of equilibrium plane TD configurations. These theoretical results are compared with Ulysses observations. It is concluded that (a) the theoretically predicted magnetic field profile agrees with the morphology of the observed profile, (b) solar wind transitions are essentially of mixed type, i.e. both ion and electron velocity distribution functions are non-Maxwellian inside the transition layer, (c) there are constraints on the orientation and magnitude of the velocity jump that can be supported across a single transition, (d) large magnetic field rotations correspond to wide transition layers, and (e) in addition to density and temperature inhomogeneities, variations in the bulk velocity are a major reason for the solar wind plasma to set up current-carrying boundary layers.

Key words: magnetic fields – plasmas – solar wind – interplanetary medium

Send offprint requests to: J. De Keyser

© European Southern Observatory (ESO) 1997

Online publication: June 30, 1998

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