The Neutral Gas and Ion Mass Spectrometer of the Mars Atmosphere and Volatile Evolution provides a large data set to explore the ion composition and structure of the Martian ionosphere. Here, the dayside measurements are used to investigate the minor ion density profiles with distinctive peaks above 150 km, revealing a systematic trend of decreasing peak altitude with increasing ion mass. We specifically focus on a subset of species including O⁺, N /CO⁺, C⁺, N⁺, He⁺, and O⁺⁺, all of which are mainly produced via direct photoionization of parent neutrals. Our analysis reveals weak or no variation with solar zenith angle (SZA) in both peak density and altitude, which is an expected result because these ion peaks are located within the optically thin regions subject to the same level of solar irradiance independent of SZA. In contrast, the solar cycle variations of peak density and altitude increase considerably with increasing solar activity, as a result of enhanced photoionization frequency and atmospheric expansion at high solar activities. He⁺ serves as an exception in that its peak density increases toward large SZA and meanwhile shows no systematic variation with solar activity. The thermospheric He distribution on Mars should play an important role in determining these observed variations. Finally, the peak altitudes for all species are elevated by at least several km within the weakly magnetized regions, possibly attributable to the suppression of vertical diffusion by preferentially horizontal magnetic fields in these regions.

中文翻译：

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白天火星电离层中次离子峰的太阳和磁控制

火星大气和挥发性演化的中性气体和离子质谱仪为探索火星电离层的离子组成和结构提供了大量数据集。在这里，日间测量被用来研究在150 km以上具有明显峰的次要离子密度曲线，揭示出随着离子质量的增加峰高降低的系统趋势。我们特别关注物种的子集，包括O ⁺，N / CO ⁺，C ⁺，N ⁺，He ⁺和O ⁺⁺，所有这些主要是通过母体中性物的直接光电离而产生的。我们的分析表明，峰密度和高度随太阳天顶角（SZA）的变化很小或没有变化，这是一个预期的结果，因为这些离子峰位于受光学辐照度相同的光学薄区域内，而与SZA无关。相反，由于高太阳活动时光电离频率和大气膨胀的增强，峰值密度和高度的太阳周期变化随太阳活动的增加而显着增加。他⁺作为一个例外，其峰值密度朝着较大的SZA增大，并且没有显示出随太阳活动的系统变化。火星上的热层He分布在确定这些观测到的变化中应起重要作用。最后，所有物种的峰值高度在弱磁化区域内至少升高了几公里，这可能归因于这些区域中优先通过水平磁场抑制了垂直扩散。