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| Titel |
Excitation of low frequency oscillations in a planetary magnetosheath by supersonic shear flow |
| VerfasserIn |
N. Borisov, M. Franz |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1023-5809
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| Digitales Dokument |
URL |
| Erschienen |
In: Nonlinear Processes in Geophysics ; 18, no. 2 ; Nr. 18, no. 2 (2011-03-21), S.209-221 |
| Datensatznummer |
250013895
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| Publikation (Nr.) |
 copernicus.org/npg-18-209-2011.pdf |
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| Zusammenfassung |
| We show that the slow magnetosonic (SM) perturbations generated in the
vicinity of the magnetopause, due to the excitation of the Kelvin-Helmholtz
(K.-H.) instability in the case of a supersonic flow velocity, are transformed
into fast magnetosonic (FM) waves which can propagate into the magnetosheath.
Under the conditions discussed in this paper, the FM wave has negative energy
in the stationary (magnetospheric) coordinate frame. Due to this the outgoing
FM wave increases the growth rate of the K.-H. instability excited at the
magnetopause. Within the linear theory, we investigate the influence of the
excited FM wave on the growth rate of the K.-H. instability. Simultaneously
we predict the transformation of the SM mode into kinetic Alfvén (KA) mode.
Thus, in general, two types of waves with different polarizations (the KA wave
and the FM wave) should appear in the magnetosheath due to the excitation of
the K.-H. instability. At the same time, the SM perturbations are only present in the localized region where the K.-H. instability is excited. To correctly describe
the excitation of waves, we use two-fluid (for electrons and ions)
magnetohydrodynamics.
This approach is more general than the ideal magnetohydrodynamics and allows us to take into account the effects
associated with the finite Larmor radius of ions. Also it can be used to investigate
the K.-H. instability in a multi-component plasma, or in the case where the
frequency of perturbations is of the order of the gyrofrequency of oxygen ions
which may occur, for example, at the magnetosheath of Mars. |
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