Spectra of Turbulence during the Dipolarization of the Magnetic Field

Аннотация

The presence of heterogeneity in turbulent processes has been analyzed, and the spectra of turbulence have been obtained for the regions before and during the dipolarization of the magnetic field in the Earth’s magnetospheric tail from the measurements of four space vehicles of the Cluster-2 mission (the event of September 21, 2005). The spectral and wavelet analysis was supplemented by the investigations of the fluctuation kurtosis for the magnetic field absolute value. In the region of the magnetic field dipolarization in the magnetospheric tail, a decreasing horizontal component of the magnetic field in parts of the tail and an increasing vertical component, kurtosis variations, the presence of strong Pc5 and Pc4 pulsations as well as direct and inverse cascades, a break in the spectra at the frequencies below the proton gyrofrequency, and a change in the character of turbulent motions at different time scales (at large time scales, the turbulent flow corresponds to the homogeneous models of Kolmogorov and Iroshnikov–Kraichnan; at smaller time scales, the turbulent flow is described by the electron magnetohydrodynamic turbulence model) have been detected. Using the measurements from different space vehicles, it was possible to estimate the velocity of the plasma flow in the tail direction.