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| Titel |
Space plasma turbulence at ion and electron scales: observations in the solar wind and Earth magnetosheath |
| VerfasserIn |
O. Alexandrova, C. Lacombe, J. Saur, A. Mangeney, V. Carbone |
| Konferenz |
EGU General Assembly 2009
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 11 (2009) |
| Datensatznummer |
250026241
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| Zusammenfassung |
| The solar wind is the most studied laboratory of space plasma turbulence. Here, at MHD
scales, the Kolmogorov’s power law f-5-3 is observed for Alfvénic fluctuations, which
dominate the turbulent spectrum. Above the spectral break in the vicinity of the ion
characteristic scales, like ion cyclotron frequency fci or ion inertial length, or Larmor radius,
the spectrum becomes steeper, ~ f-3, and the level of compressible fluctuations raises. This
range is usually called dissipation range of solar wind turbulence. Using Cluster Search Coil
magnetometer data, we show that the statistical properties of the fluctuations above the
spectral break (at f > fci) are inherent to an inertial and not to the dissipative range.
Naturally, the following question rises: at what scales turbulent energy dissipates? Perhaps at
electron scales. To verify this, we analyse the spectral shape of magnetic fluctuations at
electron scales using Cluster Spectrum Analyser data (spectra from 8Â Hz up to
4Â kHz).
The Earth’s magnetosheath is another example of magnetic turbulence in space plasmas.
Here, the Kolmogorov power law at f < fci is observed only in the flanks, however, the
small scale inertial range, with the same spectrum as in the solar wind ~ f-3, is generally
observed. We study the anisotropy of wave vector distributions of these small scale
fluctuations, using a statistical method, based on the dependence of the observed magnetic
energy at a fixed frequency on the Doppler shift for different wavenumbers. Thus we show
that this small scale fluctuations are dominated by 2D turbulence with wave vectors mainly
perpendicular to a mean field B, k-¥-« k-¥. Such anisotropy is observed up to electron scales
and it is independent on the value of plasma β, which varies in our analysis from less than 1
to about 10. |
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