EGU General Assembly 2021
© Author(s) 2023. This work is distributed under
the Creative Commons Attribution 4.0 License.

In situ observation of three-dimensional anisotropies and scalings of space plasma turbulence at kinetic scales

Tieyan Wang1, Jiansen He2, Olga Alexandrova3, Malcolm Dunlop1,4, and Denise Perrone5
Tieyan Wang et al.
  • 1RAL Space, Rutherford Appleton Laboratory, Harwell Oxford, Didcot OX11 0QX, UK (
  • 2School of Earth and Space Sciences, Peking University, Beijing 100871, People’s Republic of China
  • 3LESIA, Observatoire de Paris, Université PSL, CNRS, Sorbonne Université, Univ. Paris Diderot, Sorbonne Paris Cité, 5 place Jules Janssen, F-92195 Meudon, France
  • 4School of Space and Environment, Beihang University, Beijing 100191, People’s Republic of China
  • 5ASI—Italian Space Agency, via del Politecnico snc, I-00133 Rome, Italy

The energy distribution at wave number space is known to be anisotropic in space plasmas. At kinetic scales, the standard Kinetic Alfven Wave model predicts anisotropy scaling of kpar ∝ kperp(1/3), whereas the latest models considering the intermittency, or tearing instabilities, predict scalings such as kpar ∝ kperp(2/3) and kpar ∝ kperp(3/3). Recent numerical simulations also payed considerable attention to this issue. Based on a unified analysis of five-point structure functions of the turbulence in three kinetic simulations, Cerri et al. 2019 obtained a converging result of lpar ∝ lperp(3/3). To enrich our knowledge of the anisotropic scaling relation from an observational point of view, we conducted a statistical survey for the turbulence measured by MMS in the magnetosheath. For the 349 intervals with burst mode data, abundant evidence of 3D anisotropy at the sub-proton scale (1-100 km) is revealed by five-point second order structure functions. In particular, the eddies are mostly elongated along background magnetic field B0 and shortened in the two perpendicular directions. The ratio between eddies’ parallel and perpendicular lengths features a trend of rise then fall toward small scales, whereas the anisotropy in the perpendicular plane appears scale invariant. Moreover, over 30% of the events exhibit scaling relations close to lpar ∝ lperp(2/3). In order to explain such signature, additional factors such as intermittency caused by different coherent structures may be required in addition to the critical balance premise.

How to cite: Wang, T., He, J., Alexandrova, O., Dunlop, M., and Perrone, D.: In situ observation of three-dimensional anisotropies and scalings of space plasma turbulence at kinetic scales, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11588,, 2021.

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