Observational Quantification of Three-dimensional Anisotropies and Scalings of Space Plasma Turbulence at Kinetic Scales
Tieyan Wang, Jiansen He, Olga Alexandrova, Malcolm Dunlop, Denise Perrone
Abstract
Abstract A statistical survey of spectral anisotropy of space plasma turbulence is performed using five years of measurements from the Magnetospheric Multiscale mission in the magnetosheath. By measuring the five-point second-order structure functions of the magnetic field, we have for the first time quantified the three-dimensional anisotropies and scalings at sub-ion scales (<100 km). In the local reference frame defined with respect to local mean magnetic field , the “statistical eddies” are found to be mostly elongated along and shortened in the direction perpendicular to both and local field fluctuations. From several d i (ion inertial length) toward ∼0.05 d i , the ratio between eddies’ parallel and perpendicular lengths features a trend of rise then fall, whereas the anisotropy in the perpendicular plane appears scale-invariant. Specifically, the anisotropy relations for the total magnetic field at 0.1–1.0 d i are obtained as , and , respectively. Our results provide new observational evidence to compare with phenomenological models and numerical simulations, which may help to better understand the nature of kinetic-scale turbulence.