Observations of Vertical Reflections from the Topside Martian Ionosphere
Observations of Vertical Reflections from the Topside Martian Ionosphere
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DOI：
10.1007/s11214-006-9113-y
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发表时间：
2007-03
影响因子：
10.3
通讯作者：
E. Nielsen;H. Zou;D. Gurnett;D. Kirchner;D. Morgan;R. Huff;R. Orosei;A. Safaeinili;J. Plaut;G. Picardi
中科院分区：
文献类型：
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作者：
E. Nielsen;H. Zou;D. Gurnett;D. Kirchner;D. Morgan;R. Huff;R. Orosei;A. Safaeinili;J. Plaut;G. Picardi
火星电离层首次通过低频上部无线电波探测仪实验（MARSIS）进行了探测（Gurnett 等，2005）。首次观测到太阳天顶角小于 48 度的火星电离层密度分布。探测器频谱图通常具有单条回波痕迹，该回波痕迹由电离层在最低点方向的反射控制。利用从探测器测量得出的航天器的局部密度并使用层压技术，将频谱图转换为电子密度剖面。测量结果产生从太阳下区域到经过明暗界线的电子密度分布。最大密度随太阳自转周期而变化，表明太阳电离辐射对密度的控制。观察到与太阳耀斑相关的电子密度增加。正如理论预测的那样，最大电子密度随着太阳天顶角的变化而变化。最大密度和约 170 公里高度之间的电子密度高度分布可以通过经典查普曼层很好地近似。中性尺度高度接近10至13公里。在 180 公里以上的高度，密度偏离并大于查普曼层推断的密度。在外碱基以上的高度，密度下降近似为指数函数，标度高度在 24 至 65 公里之间。外底上方顶侧电离层的密度往往大于从适合较低高度测量的查普曼层推断的密度，这意味着在碰撞主导的光平衡区域上方的向上扩散更有效。
The Martian ionosphere has for the first time been probed by a low frequency topside radio wave sounder experiment (MARSIS) (Gurnett et al., 2005). The density profiles in the Martian ionosphere have for the first time been observed for solar zenith angles less than 48 degrees. The sounder spectrograms typically have a single trace of echoes, which are controlled by reflections from the ionosphere in the direction of nadir. With the local density at the spacecraft derived from the sounder measurements and using the lamination technique the spectrograms are inverted to electron density profiles. The measurements yield electron density profiles from the sub-solar region to past the terminator. The maximum density varies in time with the solar rotation period, indicating control of the densities by solar ionizing radiation. Electron density increases associated with solar flares were observed. The maximum electron density varies with solar zenith angle as predicted by theory. The altitude profile of electron densities between the maximum density and about 170 km altitude is well approximated by a classic Chapman layer. The neutral scale height is close to 10 to 13 km. At altitudes above 180 km the densities deviate from and are larger than inferred by the Chapman layer. At altitudes above the exobase the density decrease was approximated by an exponential function with scale heights between 24 and 65 km. The densities in the top side ionosphere above the exobase tends to be larger than the densities extrapolated from the Chapman layer fitted to the measurements at lower altitudes, implying more efficient upward diffusion above the collision dominated photo equilibrium region.