Multi Spacecraft Measurement of Anisotropic Spatial Correlation Functions at Kinetic Range in the Magnetosheath Turbulence

We investigate spatial correlation functions (SCFs) at kinetic range in the terrestrial magnetosheath because of wide angular distributions of the magnetic field fluctuations and the high Signal to Noise Ratio. We employ four point measurements of magnetic fluctuations from the Cluster and MMS concerning a spatiotemporally varying background magnetic field to constitute the two dimensional (2 D) SCFs between ion and electron scales. It is found that two populations exist in the 2 D SCFs, with the minority elongated along the perpendicular coordinate (S_⊥) and the majority of population elongated along the coordinate parallel to average magnetic field (S_||). This kind of phenomenon indicates that the distribution of magnetosheath turbulence in the wavenumber space is dominantly transverse to the background magnetic field, simultaneously partly along the field (i.e., k_⊥ >> k_||). In addition, we find that magnetosheath turbulence is the dominance of shear Alfvénic like fluctuations, and is quasi monofractal intermittent turbulence at kinetic range for both the Cluster case and the MMS case, indicating that strong spatially anisotropic fluctuations may be universal in the magnetosheath. Our observations pose new challenges to the theoretical modeling of turbulence and dissipation at kinetic range in the collisionless magnetized plasma.