Analysis of wave processes using beam-driven Langmuir/$\mathcal{Z}$-mode waveforms generated in Particle-In-Cell simulations

TL;DR

This study uses Particle-In-Cell simulations to analyze wave processes during solar radio bursts, focusing on the roles of nonlinear decay and linear mode conversion of Langmuir waves in inhomogeneous plasmas.

Contribution

It introduces a diagnostic approach with virtual satellites for detailed analysis of wave interactions, highlighting the impact of plasma density turbulence on wave dynamics.

Findings

Decay occurrence rate varies with density fluctuations and magnetization.

Turbulence significantly influences the balance between nonlinear and linear wave processes.

Results align with spacecraft observations, aiding interpretation of solar wind data.

Abstract

During Type III solar radio bursts, beam-driven upper-hybrid wave turbulence is converted into electromagnetic emissions at the fundamental plasma frequency and its harmonic, through a chain of various linear and nonlinear wave processes. In this work, we mainly investigate the relative roles and interplay of two key mechanisms: the nonlinear decay of Langmuir/$\mathcal Z$-mode waves and their linear transformations on random density fluctuations and, in particular, their mode conversion at constant frequency into electromagnetic waves. Using two-dimensional Particle-In-Cell simulations, we employ a diagnostic approach based on large ensembles of virtual satellites that record local waveforms, enabling detailed temporal and spatial characterization of wave processes in randomly inhomogeneous plasmas. This method allows robust statistical analysis and direct comparison with spacecraft observations. The study focuses on the dependence of wave dynamics on the average level of density fluctuations and the plasma magnetization. Our results quantify the occurrence rate of decay under varying physical conditions and demonstrate how developed plasma density turbulence can significantly alter the balance between nonlinear wave-wave interactions and linear wave transformations. These findings provide new insights into the mechanisms responsible for electromagnetic emissions during type III radio bursts and strengthen the connection between numerical simulations and in situ solar wind measurements, offering a valuable framework for the interpretation of future space-based waveform observations.