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| Titel |
Global scale-invariance of kinetic-scale magnetic fluctuations in solar wind turbulence as seen by CLUSTER |
| VerfasserIn |
K. H. Kiyani, S. C. Chapman, A. Turner, Yu. V. Khotyainstev, M. W. Dunlop, F. Sahraoui |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250033002
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| Zusammenfassung |
| Spacecraft measurements of magnetic fluctuations of collisionless plasma turbulence in the solar wind typically show an ‘inertial range’ of MHD turbulence with a power-law power spectra. At higher frequencies a spectral break is seen around the ion-gyroscale with a subsequent steeper power-law, indicating a cross-over to spatial-temporal scales to a ‘kinetic range’ of scaling (dissipation/dispersion range) where kinetic effects become important. We will present results from very high-frequency magnetic field data from the four Cluster II spacecraft in intervals where the spacecraft were in quasi-stationary ambient solar wind and where the instruments were operating in burst mode. The magnetic field data are from the fluxgate and search-coil magnetometers from the Cluster FGM experiment (~67Hz), and the STAFF experiment (~450 Hz). These data sets provide observations of the kinetic range range over approximately two decades in frequency. We present a robust multiscale statistical analysis focusing on power spectra, probability density functions of field fluctuations and higher-order statistics to quantify the scaling of fluctuations; as well as describing the degree of anisotropy in the fluctuations parallel and perpendicular to the average magnetic field.
Both neutral fluid and MHD turbulence share a ‘‘classic’’ statistical signature – namely an intermittent multifractal scaling seen in the higher-order statistics. MHD turbulence in the solar wind is also anisotropic due to the presence of a background field. We find that the kinetic range in contrast exhibits monoscaling behavior, i.e., a global scale invariance, and anisotropy properties distinct from that of the inertial range. This provides a strong discriminator for the physics and phenomenology of the kinetic or dissipation range in collisionless plasmas. |
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