Seasonal and Dust‐Related Variations in the Dayside Thermospheric and Ionospheric Compositions of Mars Observed by MAVEN/NGIMS
Seasonal and Dust‐Related Variations in the Dayside Thermospheric and Ionospheric Compositions of Mars Observed by MAVEN/NGIMS
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DOI：
10.1029/2021je006926
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发表时间：
2021-10
期刊：
影响因子：
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通讯作者：
N. Yoshida;N. Terada;H. Nakagawa;D. Brain;S. Sakai;Y. Nakamura;M. Benna;K. Masunaga
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文献类型：
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作者：
N. Yoshida;N. Terada;H. Nakagawa;D. Brain;S. Sakai;Y. Nakamura;M. Benna;K. Masunaga
我们报告了火星大气和挥发性演化航天器上的中性气体和离子质谱仪观测到的高度约 150 至 250 公里之间的日照火星高层大气中中性和离子物种（分别为 CO2、O 和 N2，以及 CO2+、O2+、O+ 和 N+）的季节性和与尘埃相关的变化。 CO2+ 和 O2+ 密度的正弦季节性变化清晰可见，而 O+ 的密度则不太明显。当我们将这些观察到的离子密度变化与太阳周期变化结合起来时，CO2+ 和 O+ 密度的光化学平衡模型可以很好地再现它们。此外，我们发现在区域性沙尘事件期间，MY 33 中 Ls = 342–346 的整个海拔范围内 O、O+ 和 O2+ 密度有所下降。 O 密度的降低将通过离子中性反应导致电离层中 O+ 和 O2+ 密度的降低。观察到的与季节和区域沙尘暴相关的离子和中性物质的变化也在压力坐标中得到证实。观测表明，电离层中给定压力水平下的CO2+/O+比率变化约3倍，这可以改变从火星大气中流出的离子的成分。
We report seasonal and dust‐related variations in neutral and ion species (CO2, O, and N2, and CO2+, O2+, O+, and N+, respectively) in the dayside Martian upper atmosphere between altitudes of ∼150 and ∼250 km observed by the Neutral Gas and Ion Mass Spectrometer aboard the Mars Atmosphere and Volatile Evolution spacecraft. The sinusoidal seasonal variations in CO2+ and O2+ densities are clearly identified, while that of O+ is less discernible. These observed variations in ion densities are well reproduced by a photochemical equilibrium model for CO2+ and O+ densities when we combine them with solar cycle variations. Furthermore, we find a decrease in O, O+, and O2+ densities in the whole altitude range at Ls = 342–346 in MY 33 during a regional dust event. The decrease in O density would lead to decreases in O+ and O2+ densities in the ionosphere through ion‐neutral reactions. Observed variations in ion and neutral species associated with the season and a regional dust storm are also confirmed in pressure coordinates. Observations show that the CO2+/O+ ratio at a given pressure level in the ionosphere varies by a factor of ∼3, which can modify the composition of ion outflow from the Martian atmosphere.