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Nonlinear Processes in Geophysics An interactive open-access journal of the European Geosciences Union
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Volume 14, issue 4
Nonlin. Processes Geophys., 14, 525–534, 2007
https://doi.org/10.5194/npg-14-525-2007
© Author(s) 2007. This work is licensed under
the Creative Commons Attribution-NonCommercial-ShareAlike 2.5 License.
Nonlin. Processes Geophys., 14, 525–534, 2007
https://doi.org/10.5194/npg-14-525-2007
© Author(s) 2007. This work is licensed under
the Creative Commons Attribution-NonCommercial-ShareAlike 2.5 License.

  17 Aug 2007

17 Aug 2007

Multi-point observations of intermittency in the cusp regions

M. M. Echim3,1, H. Lamy1, and T. Chang2 M. M. Echim et al.
  • 1Belgian Institute for Space Aeronomy, Avenue Circulaire 3, 1180 Bruxelles, Belgium
  • 2Kavli Institute for Astrophysics and Space Research, M. I. T., Cambridge, MA 02139, USA
  • 3Institute for Space Sciences, Atomistilor 409, 077125 Bucharest, Romania

Abstract. 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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