We used nearly 4 years of data from the Mars Atmosphere and Volatile EvolutioN orbiter to map the distribution and motion of energetic O⁺ ions (2.3–30 keV) in the Martian environment. Our analysis reveals two typical features: a strong plume of energetic O⁺ ions in the +E hemisphere at dayside, driven by the convective electric field, and a less strong tailward gathering flow of energetic O⁺ ions in the –E hemisphere at nightside. Based on previous studies, this study reveals more details on energetic O⁺ ion escape: (a) velocities for energetic O⁺ ions between bow shock and induced magnetic boundary have much larger Y-axis component, indicating that energetic O⁺ ions may not only escape along +Z-axis but also slip away on the Y-axis in MSE coordinates; (b) energetic O⁺ ions at low altitude in the –E hemisphere have little component along Y-axis, and energetic O⁺ ions at nightside in the –E hemisphere “gather” along the tail and finally escape from the planet, driven by the convective electric field and the Martian current system. Comparing the fluxes and escape rates of energetic O⁺ at different distances away from the Sun and under different solar activities, we found that the heliocentric radial distance of Mars plays a more important role in ion escape than the solar activity level.

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从火星逃逸的高能氧离子的特征：MAVEN 观察

我们使用来自火星大气和挥发性演化轨道器的近 4 年数据来绘制火星环境中高能 O ⁺离子 (2.3-30 keV)的分布和运动图。我们的分析揭示了两个典型特征：在对流电场的驱动下，日侧+ E半球的高能 O ⁺离子羽流很强，而夜间的 - E半球的高能 O ⁺离子向后聚集流不太强。基于之前的研究，这项研究揭示了更多关于高能 O ⁺离子逃逸的细节：(a)弓形激波和感应磁边界之间高能 O ⁺离子的速度有更大的Y- 轴分量，表明高能 O ⁺离子不仅可以沿 + Z轴逃逸，还可以在 MSE 坐标中沿Y轴滑走；(b) -E半球低空高能O ⁺离子沿Y轴几乎没有分量，-E半球夜侧高能O ⁺离子沿尾部“聚集”并最终逃离行星，受其驱动对流电场和火星电流系统。比较高能 O ⁺的通量和逃逸率 在离太阳不同距离和不同太阳活动下，我们发现火星的日心径向距离对离子逃逸的影响比太阳活动水平更重要。