Turbulence in the terrestrial magnetosheath: space-time correlation using the Magnetospheric Multiscale mission

TL;DR

This paper investigates the space-time correlation of magnetic field fluctuations in the terrestrial magnetosheath using MMS data, revealing anisotropic turbulence features and decorrelation mechanisms.

Contribution

It provides the first observation of the turbulence propagator in space and analyzes scale-dependent anisotropy and decorrelation processes in magnetosheath turbulence.

Findings

Clear spatial and spectral anisotropy observed.

Perpendicular modes decorrelate via sweeping or Alfvénic propagation.

Parallel mode decorrelation time is independent of wavenumber.

Abstract

Spatiotemporal correlation of magnetic field fluctuations is investigated using the Magnetospheric Multiscale mission in the terrestrial magnetosheath. The first observation of the turbulence propagator in space emerges through analysis of more than a thousand intervals. Results show clear features of spatial and spectral anisotropy, leading to a distinct behavior of relaxation times in the directions parallel and perpendicular to the mean magnetic field. Full space-time investigation of the Taylor hypothesis reveals a scale-dependent anisotropy of magnetosheath fluctuations that can be compared to the effect of flow propagation on spacecraft frame time decorrelation rates as well as with Eulerian estimates. The turbulence propagator reveals that the amplitudes of the perpendicular modes decorrelate according to sweeping or Alfv\'enic propagation mechanisms. The decorrelation time of parallel modes instead does not depend on the parallel wavenumber, which could be due to resonant interactions. Through direct observation, this study provides unprecedented insight into the space-time structure of turbulent space plasmas, while giving critical constraints for theoretical and numerical models.