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Annales Geophysicae An interactive open-access journal of the European Geosciences Union
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Volume 36, issue 5 | Copyright
Ann. Geophys., 36, 1303-1318, 2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Regular paper 02 Oct 2018

Regular paper | 02 Oct 2018

Turbulent processes in the Earth's magnetotail: spectral and statistical research

Liudmyla V. Kozak1,2, Bohdan A. Petrenko1, Anthony T. Y. Lui3, Elena A. Kronberg4,5, Elena E. Grigorenko6, and Andrew S. Prokhorenkov1 Liudmyla V. Kozak et al.
  • 1Taras Shevchenko National University of Kyiv, Kyiv, Ukraine
  • 2Space Research Institute of the National Academy of Sciences of Ukraine and State Space Agency of Ukraine, Kyiv, Ukraine
  • 3Johns Hopkins University Applied Physics Laboratory, Laurel, MD, USA
  • 4Max Planck Institute for Solar System Research, Göttingen, Germany
  • 5Department of Earth and Environmental Sciences, Ludwig Maximilian University of Munich, Munich, Germany
  • 6Space Research Institute, RAS, Russia

Abstract. We use the magnetic field measurements from four spacecraft of the Cluster-II mission (three events from 2005 to 2015) for the analysis of turbulent processes in the Earth's magnetotail. For this study we conduct the spectral, wavelet and statistical analysis. In the framework of statistical examination, we determine the kurtosis for selected events and conduct extended self-similarity evaluation (analysis of distribution function moments of magnetic field fluctuations on different scales). We compare the high-order structure function of magnetic fluctuations during dipolarization with the isotropic Kolmogorov model and three-dimensional log-Poisson model with She–Leveque parameters. We obtain power-law scaling of the generalized diffusion coefficient (the power index that varies within the range of 0.2–0.7). The obtained results show the presence of super-diffusion processes. We find the significant difference of the spectral indices for the intervals before and during the dipolarization. Before dipolarization the spectral index lies in the range from −1.68±0.05 to −2.08±0.05 ( ∼ 5∕3 according to the Kolmogorov model). During dipolarization the type of turbulent motion changes: on large timescales the turbulent flow is close to the homogeneous models of Kolmogorov and Iroshnikov–Kraichnan (the spectral index lies in the range from −2.20 to −1.53), and at smaller timescales the spectral index is in the range from −2.89 to −2.35 (the Hall–MHD model). The kink frequency is less than or close to the average value of the proton gyrofrequency.

The wavelet analysis shows the presence of both direct and inverse cascade processes, which indicates the possibility of self-organization processes, as well as the presence of Pc pulsations.

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Short summary
We analysed the turbulent processes in the Earth's magnetotail in the regions of magnetic field dipolarization and compared them with known models. We used spectral and statistical methods for analysis measurements from the Cluster-II mission. We have obtained a significant difference for turbulent processes depending on observed scales. Our results can be interesting for classification of the turbulent processes in both hydrodynamics and magnetohydrodynamics environments.
We analysed the turbulent processes in the Earth's magnetotail in the regions of magnetic field...