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| Titel |
Identification of low-frequency kinetic wave modes in the Earth's ion foreshock |
| VerfasserIn |
X. Blanco-Cano, S. J. Schwartz |
| 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 ; 15, no. 3 ; Nr. 15, no. 3, S.273-288 |
| Datensatznummer |
250012664
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| Publikation (Nr.) |
 copernicus.org/angeo-15-273-1997.pdf |
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| Zusammenfassung |
| In this work we use ion and magnetic field
data from the AMPTE-UKS mission to study the characteristics of low frequency
(ωr « Ωp) waves observed upstream of the
Earth's bow shock. We test the application of various plasma-field correlations
and magnetic ratios derived from linear Vlasov theory to identify the modes in
this region. We evaluate (for a parameter space consistent with the ion
foreshock) the Alfvén ratio, the parallel compressibility, the cross-helicity,
the noncoplanar ratio, the magnetic compression and the polarization for the two
kinetic instabilities that can be generated in the foreshock by the interaction
of hot diffuse ions with the solar wind: the left-hand resonant and the
right-hand resonant ion beam instabilities. Comparison of these quantities with
the observed plasma-field correlations and various magnetic properties of the
waves observed during 10 intervals on 30 October 1984, where the waves are
associated with diffuse ions, allows us to identify regions with Alfvénic waves
and regions where the predominant mode is the right-hand resonant instability.
In all the cases the waves are transverse, propagating at angles ≤ 33° and are elliptically polarized. Our results suggest that while
the observed Alfvén waves are generated locally by hot diffuse ions, the
right-handed waves may result from the superposition of waves generated by two
different types of beam distribution (i.e. cold beam and diffuse ions). Even
when there was good agreement between the values of observed transport ratios
and the values given by the theory, some discrepancies were found. This shows
that the observed waves are different from the theoretical modes and that mode
identification based only on polarization quantities does not give a complete
picture of the waves' characteristics and can lead to mode identification of
waves whose polarization may agree with theoretical predictions even when other
properties can diverge from those of the theoretical modes. |
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