Chaotic/turbulent cross-helical MHD dynamo: from laboratory to the Sun

TL;DR

This paper demonstrates that cross-helicity significantly influences the magnetic field spectra in chaotic MHD dynamos, linking laboratory, simulation, and solar observations, and revealing chaotic behaviors in solar magnetic activity.

Contribution

It introduces a new understanding of cross-helicity's role in MHD dynamos, supported by laboratory experiments, simulations, and solar data, within a Kolmogorov-like chaos framework.

Findings

Cross-helicity dominates magnetic field spectra in turbulent flows.

Solar magnetic field exhibits deterministic chaos during low activity periods.

Two regimes of chaotic dynamo are identified during high activity periods.

Abstract

Using the results of laboratory experiments and direct numerical simulations, as well as observations of the full-disc solar magnetic field and sunspot number dynamics, it is demonstrated that cross-helicity can dominate the frequency power spectra of the magnetic field generated by a magnetohydrodynamic (MHD) dynamo in chaotic/turbulent swirling flows. The theoretical consideration is based on a Kolmogorov-like phenomenology within the framework of the distributed chaos concept. It is shown that the solar full-disc magnetic field for the last two solar cycles with weak magnetic activity exhibits deterministic chaotic behavior concentrated around the equator. There is also observational indication that for the past periods of strong solar magnetic activity, there are two regimes of the smooth chaotic (but non-deterministic) cross-helical dynamo (high frequency and low frequency) separated by the 11-year phenomenon.