Is current disruption associated with an inverse cascade?

TL;DR

This study investigates whether current disruption in the magnetosphere involves an inverse cascade process, using advanced time-frequency analysis to reveal complex multi-scale dynamics and challenge previous simplified models.

Contribution

It applies the Hilbert-Huang transform to analyze wave modes during current disruption, providing new insights into the multi-scale and non-stationary nature of the phenomena.

Findings

Modes evolve from high to low frequencies globally

Local frequency trends indicate multi-scale physics

Inverse cascade scenario is oversimplified

Abstract

Current disruption (CD) and the related kinetic instabilities in the near-Earth magnetosphere represent physical mechanisms which can trigger multi-scale substorm activity including global reorganizations of the magnetosphere. Lui et al. (2008) proposed a CD scenario in which the kinetic scale linear modes grow and reach the typical dipolarization scales through an inverse cascade. The experimental verification of the inverse nonlinear cascade is based on wavelet analysis. In this paper the Hilbert-Huang transform is used which is suitable for nonlinear systems and allows to reconstruct the time-frequency representation of empirical decomposed modes in an adaptive manner. It was found that, in the Lui et al. (2008) event, the modes evolve globally from high-frequencies to low-frequencies. However, there are also local frequency evolution trends oriented towards high-frequencies, indicating that the underlying processes involve multi-scale physics and non-stationary fluctuations for which the simple inverse cascade scenario is not correct.