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| Titel |
Magnetic field fluctuations across the Earth’s bow shock |
| VerfasserIn |
A. Czaykowska, T. M. Bauer, R. A. Treumann, W. Baumjohann |
| 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 ; 19, no. 3 ; Nr. 19, no. 3, S.275-287 |
| Datensatznummer |
250014217
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| Publikation (Nr.) |
 copernicus.org/angeo-19-275-2001.pdf |
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| Zusammenfassung |
We present a statistical
analysis of 132 dayside (LT 0700-1700) bow shock crossings of the AMPTE/IRM
spacecraft. We perform a superposed epoch analysis of low frequency, magnetic
power spectra some minutes up-stream and downstream of the bow shock. The events
are devided into categories depending on the angle θBn
between bow shock normal and interplanetary magnetic field, and on
plasma-β. In the foreshock upstream of the quasi-parallel bow shock,
the power of the magnetic fluctuations is roughly 1 order of magnitude larger
(δB ~ 4 nT for frequencies 0.01–0.04 Hz) than upstream of
the quasi-perpendicular shock. There is no significant difference in the
magnetic power spectra upstream and downstream of the quasi-parallel bow shock;
only at the shock itself, is the magnetic power enhanced by a factor of 4. This
enhancement may be due to either an amplification of convecting upstream waves
or to wave generation at the shock interface. On the contrary, downstream of the
quasi-perpendicular shock, the magnetic wave activity is considerably higher
than upstream. Down-stream of the quasi-perpendicular low-β bow
shock, we find a dominance of the left-hand polarized component at frequencies
just below the ion-cyclotron frequency, with amplitudes of about 3 nT. These
waves are identified as ion-cyclotron waves, which grow in a low-β
regime due to the proton temperature anisotropy. We find a strong correlation of
this anisotropy with the intensity of the left-hand polarized component.
Downstream of some nearly perpendicular (θBn ≈ 90°) high-β crossings, mirror waves are identified. However, there
are also cases where the conditions for mirror modes are met downstream of the
nearly perpendicular shock, but no mirror waves are observed.
Key words. Interplanetary physics
(plasma waves and turbulence) – Magnetospheric physics (magnetosheath; plasma
waves and instabilities) |
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