Spacetime Hall-MHD turbulence at sub-ion scales: structures or waves?

TL;DR

This study investigates the nature of sub-ion scale turbulence in 2D Hall-MHD, revealing that localized structures dominate over wave phenomena, challenging the wave-based interpretation of such turbulence.

Contribution

The paper introduces Fast Iterative Filtering to analyze nonstationary signals in plasma turbulence, providing new insights into the dominant structures at sub-ion scales.

Findings

Magnetic energy is concentrated in low-frequency perturbations incompatible with known wave modes.

Signatures of whistler waves and KAWs are identified but contribute negligibly to energy.

Localized intermittent structures primarily drive sub-ion scale turbulence.

Abstract

Spatiotemporal properties of two-dimensional (2D) Hall-magnetohydrodynamic turbulence at intermediate plasma $\beta=2$ are studied by means of Fast Iterative Filtering, 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 Alfv\'en 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.