Magnetohydrodynamic Riemann problem and the structure of the magnetic reconnection layer

Journal Article · Sat Apr 01 04:00:00 EST 1995 · Journal of Geophysical Research

DOI:https://doi.org/10.1029/94JA03095· OSTI ID:166202

Wu, C C ^[1]

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1. Univ. of California, Los Angeles, CA (United States)

The author presents a complete solution for a set of magnetohydrodynamic (MHD) Riemann problems in which the upstream and downstream states have the same total pressure, and in which the normal component of the magnetic field is very small. These solutions are pertinent to subfast flows in the earth`s magnetic tail and near the magnetopause. In a coplanar situation a family of solutions exists that depend on two parameters as well as on dissipation mechanisms. In the parallel case the transverse magnetic field either does not change direction or changes the direction twice by involving two intermediate shocks. In the antiparallel case an intermediate shock is always required, except when the solution consists of two switch-off shocks. In a noncoplanar case the solution is not self-similar as a function of x/t, but continues to evolve. At early times the evolution is similar to the coplanar case. In general two time-dependent intermediate shocks are required to rotate the magnetic fields. The velocity shear has strong effect on the Riemann solution. In some cases no Riemann solution can exist because of the cavitation caused by the slow rarefaction waves. The calculated magnetopause structure resembles the observed structure for northward interplanetary magnetic field (IMF). However, for southward IMF, the MHD result shows the existence of a depletion layer, which is not supported by observations. The author also shows that on the magnetosheath side, the Walen relation, which is exact for a rotational discontinuity, can also be well satisfied by a slow shock, an intermediate shock, or the head of slow rarefaction wave. 29 refs., 19 figs.

• OSTI ID: 166202
• Journal Information: Journal of Geophysical Research, Journal Name: Journal of Geophysical Research Journal Issue: A4 Vol. 100; ISSN 0148-0227; ISSN JGREA2
• Country of Publication: United States
• Language: English

Related Subjects

66 PHYSICS
MAGNETIC RECONNECTION
MAGNETOHYDRODYNAMICS
MAGNETOPAUSE
MAGNETOTAIL
PLASMA DRIFT
RIEMANN FUNCTION
SHOCK WAVES