Determination of seasonal variations in the Martian neutral atmosphere from observations of ionospheric peak height
Determination of seasonal variations in the Martian neutral atmosphere from observations of ionospheric peak height
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根据电离层峰值高度的观测确定火星中性大气的季节变化
DOI：
10.1029/2011je003833
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发表时间：
2011-09
影响因子：
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通讯作者：
H. Zou, R. Lillis, J.-S. Wang, E. Nielsen
中科院分区：
文献类型：
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作者：
H. Zou, R. Lillis, J.-S. Wang, E. Nielsen
无线电掩星实验使我们能够测量行星大气中的电子和中性密度。在这里，我们调查了连续2个火星年（25和26）的火星全球勘测者无线电科学实验的测量结果。利用Chapman理论，我们用太阳天顶角、峰值中性标度高度、20 km处的中性密度和20 km至峰值之间的有效中性标度高度（n）来描述电离层峰值高度，发现后者是峰值高度的主要驱动因素。从掩星数据，我们观察到，在高纬度北方的电子密度峰值的高度显示出明显的季节性趋势，增加从北方夏季（Ls = 90°）到北方秋季（Ls = 180°），在n的大幅增加的驱动下，尽管在20公里的中性密度稳步下降的表面温度下降。我们发现这些趋势与LMD火星全球环流模型在20公里和130公里处的中性密度预测一致。造成20-130 km有效中性尺度高度（以及温度）增加的主要机制是，随着北方夏季变为秋季，太阳下纬度向南漂移。这驱动了火星半球间哈德利环流的季节性演变。从北方夏季到北方秋季，这一环流的向下分支导致北半球高纬度中层大气变暖加剧，导致电离层峰值及以下中性尺度高度增加，从而使电离层峰值高度增加。
Radio occultation experiments allow us to measure electron and neutral densities in planetary atmospheres. Here we investigate such measurements from the Mars Global Surveyor Radio Science experiment in 2 consecutive Martian years (25 and 26). Using Chapman theory, we parameterize the ionospheric peak altitude in terms of the solar zenith angle, neutral scale height at the peak, neutral density at 20 km and the effective neutral scale height (n) between 20 km and the peak, finding the latter to be the primary driver of peak altitude. From the occultation data, we observe that altitudes of peak electron density at high northern latitudes show a clear seasonal trend, increasing from northern summer (Ls = 90°) to northern autumn (Ls = 180°), driven by substantial increases in n, despite neutral densities at 20 km steadily decreasing as surface temperatures drop. We find these trends to be consistent with neutral density predictions from the LMD Mars Global Circulation Model at both 20 km and 130 km. The primary mechanism responsible for this increase in the 20–130 km effective neutral scale height (and hence temperature) is the southward drift in subsolar latitude as northern summer becomes autumn. This drives the seasonal evolution of the Martian interhemispheric Hadley circulation. The downward branch of this circulation leads to an increasing warming in the middle atmosphere at high north latitudes from the northern summer to the northern autumn, causing an increase in neutral scale height at and below the ionospheric peak and thus an increase in the ionospheric peak height.
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