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| Titel |
Dispersion of low frequency plasma waves upstream of the quasi-perpendicular terrestrial bow shock |
| VerfasserIn |
A. P. Dimmock, M. A. Balikhin, S. N. Walker, S. A. Pope |
| 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 ; 31, no. 8 ; Nr. 31, no. 8 (2013-08-09), S.1387-1395 |
| Datensatznummer |
250086092
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| Publikation (Nr.) |
 copernicus.org/angeo-31-1387-2013.pdf |
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| Zusammenfassung |
| Low frequency waves in the foot of a supercritical quasi-perpendicular shock
front have been observed since the very early in situ observations of the
terrestrial bow shock (Guha et al., 1972). The great attention that has been
devoted to these type of waves since the first observations is explained by
the key role attributed to them in the processes of energy redistribution in
the shock front by various theoretical models. In some models, these waves
play the role of the intermediator between the ions and electrons. It is
assumed that they are generated by plasma instability that exist due to the
counter-streaming flows of incident and reflected ions. In the second type of
models, these waves result from the evolution of the shock front itself in the
quasi-periodic process of steepening and overturning of the magnetic ramp.
However, the range of the observed frequencies in the spacecraft frame are not
enough to distinguish the origin of the observed waves. It also requires the
determination of the wave vectors and the plasma frame frequencies.
Multipoint measurements within the wave coherence length are needed for an
ambiguous determination of the wave vectors. In the main multi-point missions
such as ISEE, AMPTE, Cluster and THEMIS, the spacecraft separation is too
large for such a wave vector determination and therefore only very few case
studies are published (mainly for AMPTE UKS AMPTE IRM pair). Here we present
the observations of upstream low frequency waves by the Cluster spacecraft
which took place on 19 February 2002. The spacecraft separation during the
crossing of the bow shock was small enough to determine the wave vectors and
allowed the identification of the plasma wave dispersion relation for the
observed waves. Presented results are compared with whistler wave dispersion
and it is shown that contrary to previous studies based on the AMPTE data,
the phase velocity in the shock frame is directed downstream. The
consequences of this finding for both types of models that were developed to
explain the generation of these waves are discussed. |
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