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| Titel |
Two components of power spectral density for magnetosheath turbulence as identified from Cluster four-spacecraft measurements |
| VerfasserIn |
JianSen He, Chuanyi Tu, Eckart Marsch, Qiugang Zong, Shuo Yao, Hui Tian |
| Konferenz |
EGU General Assembly 2011
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250050280
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| Zusammenfassung |
| Cluster four-spacecraft measurements in the magnetosheath provide a good opportunity
for revealing the nature of turbulent fluctuations close to the ion scale over there.
As Cluster passed through the magnetosheath, it experienced a temporally and
spatially varying local background magnetic field (B0). For every sub-section of
B0, cross-correlations between fluctuations measured by six pairs of satellites are
projected onto the 2D-coordinate space with abscissa parallel to B0 and ordinate
perpendicular to B0. A 2D spatial correlation function (SCF) is thus established
based on the projection results of cross-correlations. The SCFs of both the density
fluctuations and the magnetic field fluctuations are estimated. We find that both of these
two SCFs are similar in pattern to each other, appearing to be composed of two
components, whereby the component parallel to B0 dominates over the perpendicular
one.
Corresponding 2D power spectral density is needed in order to know the distribution of
fluctuation energy in the wave-vector (k) space. Instead of using the conventional 2D-FFT
(Fast Fourier Transform) method, which fails to convert an observed 2D-SCF into a reliable
2D-PSD, we propose here a new method to reconstruct the 2D-PSD from the 2D-SCF based
on the projection theorem about the Fourier transform (A.K. Jain, 1989). The resulting
2D-PSD is found to consist of two components as well, with the major component being
oriented close to k-¥ and the minor one close to kll. These new findings suggest
that the turbulence energy in the magnetosheath may cascade mainly transverse
to the mean magnetic field while a small fraction of it cascades along the field. |
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