Evolution of Spectral Properties, Non-Gaussianity, and Intermittency of Plasma Turbulence Associated with Magnetotail Reconnection

Abtract: The non-ideal electric field plays a key role in turbulent plasma dissipation and particle energization at kinetic scales. However, the properties of electric field turbulence largely remains unexplored. Recently, the Kappa distribution has been associated with Langevin dynamics, which opens up a new methodology to analyze turbulent fluctuations under a unified framework of stochastic dynamics. Using measurements from the Magnetospheric Multiscale mission, we study the electric field for the first time together with the ion velocity and magnetic field to provide a cohesive description of turbulence associated with magnetotail reconnection from inertial to electron dissipation range. We show that the distribution function of turbulent fluctuations in all three fields is non-Gaussian and can be modeled with the Kappa distribution. The Kappa index and the scale-dependent kurtosis both indicate a higher degree of non-Gaussianity at smaller time scales, with a sharp transition between the inertial and sub-ion range. Multifractal analysis and the power spectrum indicate that towards electron time scales, turbulent fluctuations become less intermittent, more isotropic, and exhibit energy equipartition. These are signatures of the relaxation of turbulence towards a non-thermal quasi-equilibrium. Our results reveal new insights in the evolution of statistical properties of the non-ideal electric field in relation to those in the ion velocity and magnetic field.