Electromagnetic radiation by turbulent, magnetized and randomly inhomogeneous solar radio sources generated by electron beams

TL;DR

This study investigates the electromagnetic radiation mechanisms in solar radio bursts, revealing that only a small fraction of energy escapes as observable waves, mainly in the O-mode, with implications for interpreting spacecraft observations.

Contribution

The paper demonstrates through three approaches that most energy remains near the source in the Z-mode, refining understanding of solar radio emission modes and their observability.

Findings

Less than 10% of energy escapes as observable waves.

Most energy is in the Z-mode, near the source.

Supports interpretation of Parker Solar Probe and Solar Orbiter data.

Abstract

During Type III solar radio bursts, electromagnetic waves are radiated at plasma frequency $\omega_p$ and its harmonics by electrostatic wave turbulence generated by electron beams ejected by Sun in randomly inhomogeneous solar wind and coronal plasmas. These emissions, detected since decades by spacecraft and radiotelescopes, are split by the plasma magnetic field into three modes $\mathcal{X}$, $\mathcal{O}$ and $\mathcal{Z}$ of different dispersion, polarization and radiation properties. This work demonstrates, using three independent and converging approaches, that only a small fraction of electromagnetic energy radiated at $\omega_p$ ($\lesssim10\%$) is escaping from beam-generated radio sources, mainly as $\mathcal{O}$-mode waves and, depending on plasma conditions, as $\mathcal{X}$-mode waves. Most energy is radiated in $\mathcal{Z}$-mode and can therefore be only observed close to sources. Results have major implications for solar radio emission and provide strong support for interpretation of observations performed up to close distances to Sun by Parker Solar Probe and Solar Orbiter spacecraft.