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| Titel |
Multi-point observations of intermittency in the cusp regions |
| VerfasserIn |
M. M. Echim, H. Lamy, T. Chang |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1023-5809
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| Digitales Dokument |
URL |
| Erschienen |
In: Nonlinear Processes in Geophysics ; 14, no. 4 ; Nr. 14, no. 4 (2007-08-17), S.525-534 |
| Datensatznummer |
250012248
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| Publikation (Nr.) |
 copernicus.org/npg-14-525-2007.pdf |
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| Zusammenfassung |
| In this paper we investigate the statistical properties of
magnetic field fluctuations measured by the four Cluster spacecraft
in the cusp and close to the interface with the
magnetospheric lobes, magnetopause and magnetosheath.
At lower altitudes along the outbound orbit
of 26 February 2001, the magnetic field fluctuations recorded by all four spacecraft are random and
their Probability Distribution Functions (PDFs) are Gaussian at all
scales. The flatness parameter, F – related to the
kurtosis of the time series, is equal to 3.
At higher altitudes, in the cusp and its vicinity, closer to the interface with
the magnetopause and magnetosheath,
the PDFs from all Cluster satellites are non-Gaussian and show a clear
intermittent behavior at scales smaller than τG≈ 61 s (or
170 km). The flatness parameter increases to values
greater than 3 for scales smaller than τG.
A Haar wavelet transform enables the identification of
the "events" that produce sudden variations of the magnetic field and
of the scales that have most of the power. The LIM parameter (i.e.
normalized wavelet power) indicates that events for scales below
65 s are non-uniformly distributed
throughout the cusp passage.
PDFs, flatness and wavelet analysis show that at coarse-grained scales
larger than τG the intermittency is absent in the cusp.
Fluctuations of the magnetic energy observed during the same orbit in the magnetosheath
show PDFs that tend toward a Gaussian at scales smaller than τG
found in the cusp. The flatness analysis confirms the decreasing of
τG from cusp to magnetosheath.
Our analysis reveals the turbulent cusp as a
transition region from a non-intermittent turbulent state
inside the magnetosphere to an intermittent turbulent state in the
magnetosheath that has statistical properties
resembling the solar wind turbulence.
The observed turbulent fluctuations in the cusp
suggests a phenomenon of nonlinear interactions of plasma coherent structures
as in contemporary models of space plasma turbulence. |
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