Statistical Study of the Evolution of kappa Distribution Functions in the Plasma Sheet

The evolution with the distance to Earth of ion and electron energy distribution functions in the plasma sheet, approximated by kappa distributions, wasstudied by Stepanova and Antonova (2015, JGRA 120). Here we present results of a statistical study of the evolution of kappa distributions obtained using THEMIS datafor events of satellites located in the plasma sheet, covering between 5 and 30 Earth radi. The kappa parameter increases tailwards, for both ions and electrons. However, this behaviour is affected by the presence of geomagnetic substorms. We also analysed the magnetic fluctuations present in the data. The aim is to explore the hypothesis proposed by Navarro et al. (2014, PRL 112), for solar wind plasmas, that the observed magnetic fluctuations could be closely related to spontaneous fluctuations in the plasma, if this can be described by stable distributions. Here we present our first results on the correlation between the spectral properties of the magnetic fluctuations and the observed parameters of the kappa distributions for different distances from Earth.