Journal Article

Local Generation of Magnetosonic Waves by Ring Beam Hot Protons in the Martian Ionosphere

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

2023

Overview

Magnetosonic (MS) waves are dominant plasma waves causing severe Martian ionospheric erosion. They are generally considered to originate upstream of Martian bow shock with frequencies near the upstream proton gyrofrequency. However, whether MS waves can be locally excited lacks theoretical analysis. Here we present an event of MS waves with frequencies above and closely related to the local proton gyrofrequency in the Martian ionosphere. Concurrently, ring beam hot proton distributions are observed due to the penetration of magnetosheath protons. By employing the observed plasma and magnetic field data, the calculated linear growth rates for MS waves agree well with the observed wave power spectra, demonstrating that they can be locally excited by unstable ring beam hot protons at Mars. Our results could be of great help in understanding the excitation of MS waves in a heavy ion‐rich environment around unmagnetized planets. Plain Language Summary Magnetosonic (MS) wave is one of the most important plasma waves contributing to the Martian atmospheric loss. They are generally considered to originate upstream of the Martian bow shock. Recent observations at Mars have shown that some MS waves with frequencies near the local proton gyrofrequency were accompanied by ring/shell‐like hot proton distributions. However, whether these waves can be locally excited by such protons lacks the support of the theoretical analysis. In this letter, on the basis of linear instability analysis, we show that MS waves with frequencies well above the local proton gyrofrequency can be locally excited by unstable ring beam hot protons in the Martian ionosphere. These results advance our knowledge of the MS wave excitation in a heavy ion‐rich environment around planets without an intrinsic magnetic field. Key Points Magnetosonic waves above the local proton gyrofrequency are observed in the Martian ionosphere Ring beam hot proton distribution associated with magnetosonic waves is formed by the penetration of solar wind protons simultaneously Magnetosonic waves are locally generated by the ring beam hot protons

• Publisher: John Wiley & Sons, Inc,Wiley
• Subject: Analysis / Energy spectra / Growth rate / Gyrofrequency / Heavy ions / Ionosphere / local generation / Magnetic field / Magnetic fields / Magnetosheath / Magnetosheath protons / magnetosonic waves / Mars / Mars atmosphere / Mars ionosphere / Martian ionosphere / Planetary ionospheres / Planets / Plasma waves / Power spectra / Proton beams / Protons / ring beam hot protons / Stability analysis / Theoretical analysis / Upstream / Wave excitation / Wave power