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| Titel |
Lower-hybrid (LH) oscillitons evolved from ion-acoustic (IA)/ion-cyclotron (IC) solitary waves: effect of electron inertia |
| VerfasserIn |
J. Z. G. Ma, A. Hirose |
| 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 ; 17, no. 3 ; Nr. 17, no. 3 (2010-05-07), S.245-268 |
| Datensatznummer |
250013682
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| Publikation (Nr.) |
 copernicus.org/npg-17-245-2010.pdf |
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| Zusammenfassung |
| Lower-hybrid (LH) oscillitons reveal one aspect of geocomplexities. They have
been observed by rockets and satellites in various regions in geospace. They
are extraordinary solitary waves the envelop of which has a relatively longer
period, while the amplitude is modulated violently by embedded oscillations
of much shorter periods. We employ a two-fluid (electron-ion) slab model in a
Cartesian geometry to expose the excitation of LH oscillitons. Relying on a
set of self-similar equations, we first produce, as a reference, the
well-known three shapes (sinusoidal, sawtooth, and spiky or bipolar) of
parallel-propagating ion-acoustic (IA) solitary structures in the absence of
electron inertia, along with their Fast Fourier Transform (FFT) power
spectra. The study is then expanded to illustrate distorted structures of the
IA modes by taking into account all the three components of variables. In
this case, the ion-cyclotron (IC) mode comes into play. Furthermore, the
electron inertia is incorporated in the equations. It is found that the
inertia modulates the coupled IA/IC envelops to produce LH oscillitons. The
newly excited structures are characterized by a normal low-frequency IC
solitary envelop embedded by high-frequency, small-amplitude LH oscillations
which are superimposed upon by higher-frequency but smaller-amplitude IA
ingredients. The oscillitons are shown to be sensitive to several input
parameters (e.g., the Mach number, the electron-ion mass/temperature ratios,
and the electron thermal speed). Interestingly, whenever a LH oscilliton is
triggered, there occurs a density cavity the depth of which can reach up to
20% of the background density, along with density humps on both sides of the
cavity. Unexpectedly, a mode at much lower frequencies is also found beyond
the IC band. Future studies are finally highlighted. The appendices give a
general dispersion relation and specific ones of linear modes relevant to all
the nonlinear modes encountered in the text. |
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