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| Titel |
The statistics of foreshock cavities: results of a Cluster survey |
| VerfasserIn |
L. Billingham, S. J. Schwartz, D. G. Sibeck |
| 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 ; 26, no. 12 ; Nr. 26, no. 12 (2008-11-20), S.3653-3667 |
| Datensatznummer |
250016299
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| Publikation (Nr.) |
 copernicus.org/angeo-26-3653-2008.pdf |
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| Zusammenfassung |
| We use Cluster magnetic field, thermal ion, and energetic particle
observations upstream of the Earth's bow shock to investigate the occurrence
patterns of foreshock cavities. Such cavities are thought to form when
bundles of magnetic field connect to the quasi-parallel bow shock.
Shock-processed suprathermal ions can then stream along the field, back
against the flow of the solar wind. These suprathermals enhance the pressure
on shock-connected field lines causing them to expand into the surrounding
ambient solar wind plasma. Foreshock cavities exhibit depressions in magnetic
field magnitude and thermal ion density, associated with enhanced fluxes of
energetic ions. We find typical cavity duration to be few minutes with
interior densities and magnetic field magnitudes dropping to ~60% of
those in the surrounding solar wind. Cavities are found to occur
preferentially in fast, moderate magnetic field strength solar wind streams.
Cavities are observed in all parts of the Cluster orbit upstream of the bow
shock. When localised in a coordinate system organised by the underlying
physical processes in the foreshock, there is a systematic change in
foreshock cavity location with IMF cone angle. At low (high) cone angles
foreshock cavities are observed outside (inside) the expected upstream
boundary of the intermediate ion foreshock. |
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