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| Titel |
Low-frequency magnetic field fluctuations in Venus' solar wind interaction region: Venus Express observations |
| VerfasserIn |
L. Guicking, K.-H. Glassmeier, H.-U. Auster, M. Delva, U. Motschmann, Y. Narita, T. L. Zhang |
| 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. 4 ; Nr. 28, no. 4 (2010-04-15), S.951-967 |
| Datensatznummer |
250016817
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| Publikation (Nr.) |
 copernicus.org/angeo-28-951-2010.pdf |
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| Zusammenfassung |
| We investigate wave properties of low-frequency magnetic field
fluctuations in Venus' solar wind
interaction region based on the measurements made on board the Venus
Express spacecraft. The orbit geometry is very suitable to
investigate the fluctuations in Venus' low-altitude magnetosheath
and mid-magnetotail and provides an opportunity for a comparative
study of low-frequency waves at Venus and Mars. The
spatial distributions of the wave properties, in particular in the
dayside and nightside magnetosheath as well as in the tail and
mantle region, are similar to observations at Mars. As both planets
do not have a global magnetic field, the interaction process of the
solar wind with both planets is similar and leads to similar
instabilities and wave structures. We focus on the spatial
distribution of the wave intensity of the fluctuating magnetic field and
detect an enhancement of the intensity in the dayside magnetosheath
and a strong decrease towards the terminator. For a detailed
investigation of the intensity distribution we adopt an
analytical streamline model to describe the plasma flow around
Venus. This allows displaying the evolution of the intensity along
different streamlines. It is assumed that the waves are generated
in the vicinity of the bow shock and are convected
downstream with the turbulent magnetosheath flow.
However, neither the different Mach numbers upstream and downstream
of the bow shock, nor the variation of the cross sectional area and
the flow velocity along the streamlines play probably an important role
in order to explain the observed concentration of wave intensity in the
dayside magnetosheath and the decay towards the nightside
magnetosheath. But, the concept of freely evolving or decaying turbulence is in good
qualitative agreement with the observations, as we observe a power law decay
of the intensity along the streamlines. The observations support the assumption of
wave convection through the magnetosheath, but reveal at the same time
that wave sources may not only exist at the bow shock, but also in the magnetosheath. |
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