Turbulence in the terrestrial magnetosheath: space-time correlation using MMS

Spatiotemporal correlation of magnetic field fluctuations is investigated using theMagnetospheric Multiscale mission in the terrestrial magnetosheath. The first observation ofthe turbulence propagator emerges through analysis of more than a thousand intervals.Results show clear features of spatial and spectral anisotropy, leading to a distinct behavior ofrelaxation times in the directions parallel and perpendicular to the mean field.The full space-time investigation of the Taylor hypothesis presents a scale-dependentanisotropy of the magnetosheath when compared to characteristic flow propagation time andwith Eulerian estimates.The turbulence propagator reveals that the amplitudes of the perpendicular modes decorrelateaccording to sweeping or Alfvénic mechanisms. The decorrelation time of parallel modesinstead does not depend on the parallel wavenumber which could be due to resonantinteractions.This study provides unprecedented observations into the space-time structure of turbulentspace plasmas, also giving critical constraints for theoretical and numerical models.