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| Titel |
On arc-polarized structures in the solar wind |
| VerfasserIn |
B. U. Ö. Sonnerup, S. E. Haaland, G. Paschmann |
| 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 ; 28, no. 6 ; Nr. 28, no. 6 (2010-06-08), S.1229-1248 |
| Datensatznummer |
250016840
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| Publikation (Nr.) |
 copernicus.org/angeo-28-1229-2010.pdf |
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| Zusammenfassung |
| A theoretical model is proposed to account for
some of the behavior of arc-polarized magnetic structures seen in the solar
wind. To this end, an exact analytical solution is developed that
describes infinite plane wave trains of arbitrary amplitude in a plasma
governed by ideal Hall MHD. The main focus is on intermediate-mode wave trains,
which display double-branched magnetic hodogram signatures similar to those
seen in the solar wind. The theoretically derived hodograms have field
rotation in the ion-polarized sense at a slightly depressed field magnitude
on one branch and an electron-polarized rotation at a slightly enhanced
field magnitude on the other branch. The two branches are joined at the two
"turning points", at which
the normal flow is exactly Alfvénic. The behavior
is accounted for in terms of the opposite dispersive properties of ion and
electron whistlers. The hodograms derived from the theory are shown to
compare favorably with those of one event, observed by the Cluster
spacecraft near the ecliptic plane, and one event at high heliographic
latitude observed by the Ulysses spacecraft. However, these two observed
structures comprise only a single full wave period, approximately from one
turning point to the other and then back again. The theory can be used to
predict propagation direction (away from, or towards, the sun) from magnetic
data alone, provided the sign of the magnetic field component along the wave
normal can be reliably determined. Under the same condition, it also
predicts whether the ion-polarized branch should precede or follow the
electron-polarized branch. Both behaviors are seen in the solar wind. The
major shortcoming of the theory is that it fails to reproduce the observed
saw-tooth like time series for the magnetic field, in which the field
rotation is rapid in the ion sense and slow in the electron sense. Instead,
the theory gives about the same rotation rates. Possible explanations for
this discrepancy are discussed. Also discussed is the fact that the magnetic
field measurements by Cluster, while giving high quality determinations of
normal direction and normal field component for each of the four spacecraft,
indicate a reversal of the normal field component and the predicted
propagation sense during the event, as well as a wide spread in the four
normal vector orientations. |
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