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| Titel |
Foreshock density holes in the context of known upstream plasma structures |
| VerfasserIn |
M. Wilber, G. K. Parks, K. Meziane, N. Lin, E. Lee, C. Mazelle, A. Harris |
| 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 (2008-11-26), S.3741-3755 |
| Datensatznummer |
250016306
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| Publikation (Nr.) |
 copernicus.org/angeo-26-3741-2008.pdf |
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| Zusammenfassung |
| We present case examples of foreshock density holes and results from
a statistical survey, which provide additional characterizations of these
recently-described structures.
Specific effort is made to place these objects into context with well-studied
foreshock phenomena, such as hot flow anomalies (HFAs) and
large-amplitude magnetic pulsations (SLAMS).
Density holes are observed during higher-than-average solar wind speeds
(~620 km s−1), have well-correlated density and magnetic field
intensities, and anti-correlated density and temperature variations.
Like HFAs, these structures occur over a wide range of foreshock geometries,
suggesting that this is not a determining factor.
They are embedded within IMF current sheets, but their cross-structure magnetic
shears are considerably lower than for HFAs.
When the Cluster spacecraft are widely separated, they are able to measure
structure time development, with substantial changes occurring over 10s of
seconds, confirming an earlier case study, and possibly indicating short
lifetimes as well.
We find that density holes can occur in the absence of strong upstream magnetic
pulsations and/or density enhancements, which rules out a "wake
effect" as the sole explanation for their formation.
Most important is the observation that the observed solar wind motional
electric fields tend to have components pointing away from the embedding
IMF current sheets.
Density holes have no connection with magnetic holes and foreshock
cavities, and appear not to be early-stage or weakly-formed HFAs. |
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