No abstract

We use kappa distributions to model thousands of ion and electron flux spectra along the plasma sheet and analyze the variation of the spectral index κ and the temperature T in this region. We find that κ distributions are ubiquitous and fit well ion and electron flux spectra during quiet times, and during the expansion and recovery phases of substorms. Near Earth, and up to ∼12 RE, the κ indices are different than the rest of the plasma sheet, both for ions (κi) and electrons (κe). There is a significant dawn‐dusk asymmetry in κi toward the tail, which is enhanced during substorms. The ions also exhibit a permanent temperature asymmetry, determined by a colder dawnside. The whole tail becomes hotter during substorms, but it appears that most of the energy is deposited near Earth.

Abstract. Study of the plasma turbulence in the central plasma sheet was performed using the Interball-Tail satellite data. Fluctuations of the plasma bulk velocity in the plasma sheet were deduced from the measurements taken by the Corall instrument for different levels of geomagnetic activity and different locations inside the plasma sheet. The events that satisfied the following criteria were selected for analysis: number density 0.1-10 cm −3 , ion temperature T ≥0.3 keV, and average bulk velocity ≤100 km/s. It was found that the plasma sheet flow generally appears to be strongly turbulent, i.e. is dominated by fluctuations that are unpredictable. Corresponding eddy-diffusion coefficients in Y-and Z-direction in the GSM coordinate system were derived using the autocorrelation time and rms velocity. Statistical studies of variation of the eddy-diffusion coefficients with the location inside the plasma sheet showed a significant increase in these coefficients in the tailward direction. During substorms this dependence shows strong increase of eddy-diffusion in the central part of the plasma sheet at the distances of 10-30 Earth's radii. This effect is much stronger for Y-components of the eddy-diffusion coefficient, which could be related to the geometry of the plasma sheet, allowing more room for development of eddies in this direction.