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| Titel |
Relation between current sheets and vortex sheets in stationary incompressible MHD |
| VerfasserIn |
D. H. Nickeler, T. Wiegelmann |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
0992-7689
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| Digitales Dokument |
URL |
| Erschienen |
In: Annales Geophysicae ; 30, no. 3 ; Nr. 30, no. 3 (2012-03-16), S.545-555 |
| Datensatznummer |
250017200
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| Publikation (Nr.) |
 copernicus.org/angeo-30-545-2012.pdf |
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| Zusammenfassung |
| Magnetohydrodynamic configurations with strong localized current concentrations
and vortices play an important role in the dissipation of energy in
space and astrophysical plasma. Within this work we investigate the
relation between current sheets and vortex sheets in incompressible,
stationary equilibria. For this approach it is helpful that the similar
mathematical structure of magnetohydrostatics and stationary incompressible
hydrodynamics allows us to transform static equilibria into stationary ones.
The main control function for such a transformation is the profile of the
Alfvén-Mach number MA, which is always constant along magnetic field
lines, but can change from one field line to another. In the case of a
global constant MA, vortices and electric current concentrations
are parallel. More interesting is the nonlinear case, where MA varies
perpendicular to the field lines. This is a typical situation at boundary
layers like the magnetopause, heliopause, the solar wind flowing around
helmet streamers and at the boundary of solar coronal holes.
The corresponding current and vortex sheets show in some cases also an alignment,
but not in every case. For special density distributions in 2-D, it is possible to have
current but no vortex sheets. In 2-D, vortex sheets of field aligned-flows
can also exist without strong current sheets, taking the limit
of small Alfvén Mach numbers into account. The current sheet can vanish if
the Alfvén Mach number is (almost) constant and the density gradient is large
across some boundary layer. It should be emphasized that the
used theory is not only valid for small Alfvén Mach numbers MA << 1, but also for
MA ≲ 1. Connection to other theoretical approaches and observations and
physical effects in space plasmas are presented. Differences in the various aspects of theoretical
investigations of current sheets and vortex sheets are given. |
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