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

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 highorder structure function of magnetic fluctuations during dipolarization with the isotropic Kolmogorov model and threedimensional 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 superdiffusion 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.

Nighttime Magnetic Perturbation Events Observed in Arctic Canada: 1. Survey and Statistical Analysis

“…Non‐self‐similar scaling of PDFs of the fluctuations in the flow or magnetic field was used to identify intermittent turbulence (Weygand et al, ). The magnetic fluctuations in the plasma sheet were found to be consistent with expectations for an intermittently turbulent MHD fluid (Kozak et al, ; Weygand et al, ). Stepanova et al () found that the PDF of the PC index (polar cap index charactering the energy supply from the solar wind into the magnetosphere) could be fitted by two log‐normal distributions.…”

The Effect of Solar-Wind Turbulence on Magnetospheric Activity

“…The solar wind and the magnetosphere are high Reynolds number plasma environments [45], both showing scaleinvariant dynamics and power-law PSDs. Several studies have been carried out to investigate the turbulent nature of the solar wind (e.g., [32,36]; and references therein) and the magnetosphere (e.g., [46][47][48][49][50][51]) separately, invoking turbulence and a SOC approach to describe the dynamics of the two plasma environments, respectively. At this stage, an obvious question arises: whether SOC is different from turbulence.…”

“…It must be noted, however, that beside the strong connection existing between the solar wind and the magnetosphere via reconnection processes, the solar wind and the magnetosphere are both high Reynolds number plasmas [45]. As a result, we would expect that not only the solar wind but also the magnetosphere shows a scale-invariant dynamics and powerlaw PSD (e.g., [46][47][48][49][50][51]). On the other hand, geomagnetic indices are widely used to study the magnetospheric output and are indicative of the most important magnetospheric current systems.…”

Severe Magnetic Fluctuations in the Near‐Earth Magnetotail: Spectral Analysis and Dependence on Solar Activity

“…A main focus of this study is the spectral characteristics of severe magnetic fluctuations associated with field dipolarization in the near-Earth magnetotail. Compared with previous spectral studies (e.g., Kozak et al, 2018;Shiokawa et al, 2005) associated with field dipolarization, the present study was focused on severe magnetic fluctuations defined as B ∕B > 0.5. Then, as explained in section 2, the signature of dipolarization was used to clarify the timing of substorm onsets.…”

“…Ono et al (2009) showed that these magnetic fluctuations can induce an electric field that further accelerates ions nonadiabatically. Previous studies have also reported the spectral properties of these magnetic fluctuations (e.g., Kozak et al, 2018;Lui et al, 1992;Nishitani & Oguti, 1988;Ohtani et al, 1998;Shiokawa et al, 2005). The Active Magnetospheric Particle Tracer Explorers/Charge Composition Explorer (AMPTE/CCE), Spacecraft Charging at High Altitude (SCATHA), and GEOTAIL satellites used in those studies provided magnetic field measurements at ∼8.8, ∼7.8, and 8-11 R E , respectively.…”