Langmuir Wave Excitation in Solar-wind Magnetic Holes

TL;DR

This paper presents a model explaining how magnetic holes in the solar wind can excite Langmuir waves through changes in electron velocity distributions, supported by Solar Orbiter data.

Contribution

It introduces a novel model linking magnetic-moment conservation violations to Langmuir wave excitation in magnetic holes, validated with spacecraft observations.

Findings

Model successfully explains Langmuir wave excitation in magnetic holes.

Observational data from Solar Orbiter supports the model's predictions.

Magnetic holes are confirmed as sites for Langmuir wave generation in the solar wind.

Abstract

Magnetic holes are structures commonly observed in various space plasma environments throughout the solar system, including the solar wind. These structures are characterized by a localized decrease in magnetic field strength, coincident with an increase in plasma density. Previous observational studies in the solar wind link the presence of Langmuir waves to magnetic holes, suggesting a strong correlation between these phenomena. We develop a model based on magnetic-moment conservation and its violation to explain the excitation of Langmuir waves in magnetic holes. Our model illustrates that magnetic holes induce changes in the electron velocity distribution function that emit electrostatic Langmuir waves due to the bump-on-tail instability. Using data from the Solar Orbiter spacecraft, we provide a comprehensive analysis of this process and test our predictions with observations. The consistency between the model and observations indicates that our proposed process is a viable mechanism for producing Langmuir waves in magnetic holes in the solar wind.