Global dust storms (GDS) are an important dynamical phenomenon of the Martian lower atmosphere but are known to have important impacts on the Martian middle/upper atmosphere and ionosphere. Despite extensive studies over the past several decades, how the composition of the Martian ionosphere is modified during the GDS has only been studied from a theoretical point of view. Here we present for the first time the observations of the compositional variation of the Martian ionosphere during the GDS in 2018, using the ion density measurements made by the Neutral Gas and Ion Mass Spectrometer onboard the Mars Atmosphere and Volatile Evolution. At a representative altitude of 170 km, the variations of ionospheric species during the GDS show either enhancement (, Ar⁺, , H₂O⁺, , ArH⁺) or depletion (, O⁺, /CO⁺, OH⁺). Despite the apparent diversity, the observations are mostly understandable within the established framework of ionospheric chemistry on Mars, which further demonstrates that the variation of ion species during the GDS is a good diagnostic of the variation of relevant neutral species in the thermosphere. In particular, the observed ionospheric variation strongly supports a scenario that H₂O is substantially enhanced in the Martian thermosphere during the GDS. However, the variations of and are inconsistent with predictions from ionospheric chemistry and require further investigation.

中文翻译：

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火星电离层对2018年全球沙尘事件的物种依赖性反应

全球沙尘暴（GDS）是火星低层大气的重要动力现象，但已知会对火星中/高层大气和电离层产生重要影响。尽管在过去的几十年中进行了广泛的研究，但仅从理论角度研究了GDS期间如何改变火星电离层的组成。在这里，我们首次使用火星大气层和挥发性演化过程中的中性气体和离子质谱仪进行的离子密度测量，对2018年GDS期间火星电离层的成分变化进行了观测。在170公里的代表性高度，电离层物种的GDS期间中的变化或者显示增强（中，Ar ⁺，，H ₂O ⁺，ArH ⁺或耗尽（，O ⁺，/ CO ⁺，OH ⁺）。尽管表面上存在明显的多样性，但在火星上电离层化学的既定框架内，这些观察结果大多数是可以理解的，这进一步表明，GDS期间离子种类的变化可以很好地诊断热层中相关中性物质的变化。特别是，观测到的电离层变化强烈支持了在GDS期间火星热层中H ₂ O显着增强的情况。然而，的变化和 与电离层化学的预测不一致，需要进一步研究。