Spacetime Hall-MHD Turbulence at Sub-ion Scales: Structures or Waves?

Spatiotemporal properties of two-dimensional (2D) Hall-magnetohydrodynamic (MHD) turbulence at intermediate
plasma β = 2 are studied by means of Fast Iterative Filtering (FIF), a new technique for the decomposition of
nonstationary nonlinear signals. Results show that the magnetic energy at sub-ion scales is concentrated in
perturbations with frequencies smaller than the ion-cyclotron (IC) frequency and with polarization properties that
are incompatible with both kinetic Alfvén waves (KAWs) and IC waves. At higher frequencies, we clearly identify
signatures of both whistler waves and KAWs; however, their energetic contribution to the magnetic power
spectrum is negligible. We conclude that the dynamics of 2D Hall-MHD turbulence at sub-ion scales is mainly
driven by localized intermittent structures, with no significant contribution of wavelike fluctuations