作者: Tieyan Wang , Jiansen He , Olga Alexandrova , Malcolm Dunlop , Denise Perrone
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摘要: A statistical survey of spectral anisotropy space plasma turbulence is performed using five years measurements from MMS in the magnetosheath. By measuring five-point second-order structure functions magnetic field, we have for first time quantified three-dimensional anisotropies and scalings at sub-ion-scales ($<$ 100 km). In local reference frame $(\hat L_{\perp}, \hat l_{\perp}, l_{\parallel})$ defined with respect to mean field $\boldsymbol {B}_0$ (Chen et al. 2012), "statistical eddies" are found be mostly elongated along shortened direction perpendicular both fluctuations. From several $d_i$ (ion inertial length) toward $\sim$ 0.05 $d_i$, ratio between eddies' parallel lengths features a trend rise then fall, whereas plane appears scale-invariant. Specifically, relations total 0.1-1.0 obtained as $l_{\parallel} \simeq 2.44 \cdot l_{\perp}^{0.71}$, $L_{\perp} 1.58 l_{\perp}^{1.08}$, respectively. Our results provide new observational evidence compare phenomenological models numerical simulations, which may help better understand nature kinetic scale turbulence.