Observations of Ion Cyclotron Waves Upstream from the Martian Bow Shock

Q4 Physics and Astronomy
Li Jia-wei , Yang Lei , Wu De-jin , Dai Cun-li , Li Jian-ping , Xiang Liang , Luo Qing-yu , Cheng Zheng-wei
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引用次数: 0

Abstract

Ion cyclotron waves are widely present upstream from the Martian bow shock, with frequencies near the local proton cyclotron frequency in the spacecraft frame. The waves propagate quasi-parallel to the background magnetic field, and are associated with the solar wind picking up newly-ionized hydrogen from the Martian exosphere. In this work, a typical ion cyclotron wave event was observed by MAVEN (Mars Atmosphere and Volatile Evolution) probe upstream from the Martian bow shock. The further MVA (minimum variance analysis) results for this event show that the magnetic field perturbations are left-handed polarized and propagate quasi-parallel (the propagation angle θ = 12.37) to the background magnetic field. The relationship between the plasma perturbations and magnetic field perturbations is theoretically derived for slow magnetosonic, Alfv{\'e}n, and fast magnetosonic waves based on the magnetohydrodynamic theory. If we take the wave propagation angle θ = 12.37 estimated from the MVA method, the theoretically expected density perturbation and velocity perturbation along the background magnetic field are in serious disagreement with the MAVEN data. Through fitting the plasma density perturbation, velocity perturbation, and magnetic field perturbation, it is found that the ion cyclotron wave event can be explained by the superposition of oblique fast magnetosonic waves with a propagation angle of 63 relative to the background magnetic field and parallel propagating Alfv{\'e}n waves. The results are helpful to further understand the physical nature of the observed ion cyclotron wave-related perturbations upstream from the Martian bow shock, and have guiding implications for the re-modeling and numerical simulation of the plasma physical processes therein.
火星弓形激波上游离子回旋波的观测
离子回旋波广泛存在于火星弓形激波的上游,其频率接近航天器框架内的本地质子回旋波频率。这些波与背景磁场近乎平行地传播,并且与太阳风从火星外逸层吸收新电离的氢有关。在这项工作中,MAVEN(火星大气与挥发物演化)探测器在火星弓形激波上游观测到一个典型的离子回旋波事件。对该事件进一步的最小方差分析结果表明,磁场扰动是左极化的,传播角θ = 12.37°)与背景磁场近似平行。基于磁流体动力学理论,推导了慢磁子、Alfv{\'e}n和快磁子的等离子体扰动与磁场扰动之间的关系。如果取MVA法估算的波传播角θ = 12.37°,则理论上预期的密度摄动和速度摄动沿背景磁场方向的摄动与MAVEN数据严重不符。通过拟合等离子体密度摄动、速度摄动和磁场摄动,发现离子回旋波事件可以用相对于背景磁场传播角为63°的倾斜快速磁声波与平行传播的Alfv{\'e}n波的叠加来解释。研究结果有助于进一步理解火星弓形激波上游观测到的离子回旋波相关扰动的物理性质,并对其中等离子体物理过程的重新建模和数值模拟具有指导意义。
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来源期刊
Chinese Astronomy and Astrophysics
Chinese Astronomy and Astrophysics Physics and Astronomy-Astronomy and Astrophysics
CiteScore
0.70
自引率
0.00%
发文量
20
期刊介绍: The vigorous growth of astronomical and astrophysical science in China led to an increase in papers on astrophysics which Acta Astronomica Sinica could no longer absorb. Translations of papers from two new journals the Chinese Journal of Space Science and Acta Astrophysica Sinica are added to the translation of Acta Astronomica Sinica to form the new journal Chinese Astronomy and Astrophysics. Chinese Astronomy and Astrophysics brings English translations of notable articles to astronomers and astrophysicists outside China.
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