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| Titel |
Rapid density fluctuations in the solar wind |
| VerfasserIn |
P. J. Kellogg, T. S. Horbury |
| 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 ; 23, no. 12 ; Nr. 23, no. 12 (2005-12-23), S.3765-3773 |
| Datensatznummer |
250015439
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| Publikation (Nr.) |
 copernicus.org/angeo-23-3765-2005.pdf |
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| Zusammenfassung |
| Electron density fluctuations (up to 2.5 Hz) in the solar wind have been
studied, using the EFW experiment on the Cluster spacecraft, which measures
density through measurements of the biased probe potentials relative to the
spacecraft. The density fluctuation spectra obtained from the EFW probe
potential variations are compared to earlier, OGO 5, measurements of ion
density fluctuations and ISEE measurements of electron density fluctuations,
and are consistent with them. The electric fields corresponding to the
electron density fluctuations are extremely small compared with what would
be obtained if the electron fluctuations were not cancelled out by nearly
equal ion density fluctuations. This is consistent with the nature of ion
acoustic waves. In agreement with ISEE work, the fluctuations are
proportional to the ambient density. Correlation with magnetic fluctuations
is weak, essentially nonexistent during part of the period studied. This
might be expected as magnetic fluctuations are known to be nearly
incompressible, but even the correlation with fluctuations in the magnitude
of B is very small. However, many structures which apparently are pressure
balance structures are found. Pressure balance structures are the nearly
perpendicular propagation limit of ion acoustic waves.
As ion acoustic waves are strongly damped in plasmas like the solar wind at
least if the plasma is taken as Maxwellian, it has always been a puzzle as
to why they are found there. We speculate that these waves are created by
mode conversion from magnetic fluctuations, and may represent part of the
dissipation process for these. |
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