Processes in the Current Disruption Region: From Turbulence to Dispersion Relation

Abstract

Using measurements from Cluster‐II space mission, we compared the characteristics of the fluctuations of the magnetic field magnitude and the Bz component in the current disruption (CD) regions. We used fast Fourier transform, statistical, and wavelet analysis, and wave surveyor technique on the multispacecraft measurements. Among the obtained results one can note the presence of spectral breaks in both the magnetic field magnitude and the Bz component at frequencies smaller or equal to the proton gyrofrequency. The numerical values of the spectral index for the magnetic field magnitude and for the Bz component are similar, and the nature of the turbulent processes is close to that of the homogeneous magnetohydrodynamic (MHD) (the spectral index varies from −2.00 to −1.31) on the large time scale and resembles Hall‐MHD (the spectral index varies from −2.33 to −2.99) on the smaller time scales. The kurtosis results are consistent with those of the spectral analysis. From wavelet technique, we detected powerful Pc4 and Pi1 pulsations, along with cascade features both for the magnetic field magnitude and for its z‐component. The dispersion ratios also indicate the presence of nonlinear energy cascade processes in CD regions. We have found that the pulsations observed for magnetic pressure are also present in thermal proton and electron pressures although their powers differ considerably. For the dynamic helium and oxygen pressures, and also for the thermal pressures of these components, only pulsations in the high‐frequency region are revealed.

Turbulent dipolarization regions in the Earth’s magnetotail: ion fluxes and magnetic field changes

“…The dipolarization fronts can be detached as (i) isolated (observed over a few minutes) (Nakamura et al, 2002;Runov et al, 2009;Runov et al, 2011) and (ii) "secondary" (with duration up to hours), which are associated with the system of currents (wedge) during substorm generation (Sergeev et al, 2012). The properties and behaviour of various ion fluxes during magnetic field dipolarization, which are characterized by turbulence and significant variability of plasma parameters, were considered in the studies by Kozak et al (2018b), Kozak et al (2018a), Kozak et al (2018), Kozak et al (2020), Kozak et al (2021).…”