Journal Article

A Parametric Study of Locally Generated Magnetosonic Waves by Ring‐Beam Hot Protons in the Martian Heavy Ion‐Rich Environment

Cui, Jun, Liu, Xu, Cao, Jinbin, Chen, Zuzheng, Wang, Jing, Yu, Jiang

2024

Overview

Magnetosonic (MS) waves with frequencies above the proton gyrofrequency can be locally generated by ring‐beam protons in the Martian heavy ion‐rich ionosphere. In this study, we conduct a parametric analysis to investigate the effects of heavy ion concentrations, energy (Erb), and angle (αrb) of ring‐beam protons, and wave normal angle on the excitation features of Martian ionospheric MS waves. We find the growth rates and frequency range of MS waves decrease by including O+ and O2+ ions but are insensitive to their relative concentrations. With increasing Erb or αrb, the growth rates of MS waves show a general dropping tendency. Meanwhile, their frequency and wavenumber range are almost unaffected by increasing Erb but shrink to a narrower range mainly distributed in high frequencies by increasing αrb. Unstable MS waves expand to a wider wavenumber range but shrink to a narrower frequency range as they become more oblique. Plain Language Summary Magnetosonic (MS) waves are highly compressible electromagnetic emissions in space. Generally, they are locally excited by ring‐like hot protons in plasmas that lack heavy ions. However, a recent study reveals that they can also be locally excited by ring‐beam protons in the Martian heavy ion‐rich ionosphere. Motivated by these differences, we conduct a detailed parametric analysis to investigate how the heavy ion concentrations, the energy and angle of ring‐beam protons, and the wave normal angle affect the dispersion relation and growth rate of Martian MS wave. We find that O+ and O2+ ions lower the growth rates and frequency range of MS waves but the effects of their relative concentrations are insignificant. In addition to the heavy ions, the excitation features of MS waves strongly depend on the wave normal angle and the distribution properties of ring‐beam protons. These results deepen our understanding of the MS wave excitation features in the unmagnetized planet environment with plentiful heavy ions. Key Points O+ and O2+ ions lower the growth rates and frequency range of Magnetosonic (MS) waves but the effects of their relative concentrations are insignificant The growth rates of MS waves show a general dropping tendency with increasing ring‐beam energy or angle Unstable MS waves expand to a wider wavenumber range but shrink to a narrower frequency range as they become more oblique

• Publisher: John Wiley & Sons, Inc,Wiley
• Subject: Compressibility / dispersion relation / Frequency ranges / Growth rate / growth rates / Gyrofrequency / Heavy ions / Ionosphere / Ions / magnetosonic waves / Martian heavy ion‐rich environment / Parametric analysis / Proton beams / Protons / ring‐beam hot protons / Wave dispersion / Wave excitation / Wavelengths