Vertical sheets of dense plasma in the topside Martian ionosphere
Vertical sheets of dense plasma in the topside Martian ionosphere
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DOI：
10.1029/2006je002723
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发表时间：
2007-02
影响因子：
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通讯作者：
E. Nielsen;X.‐D. Wang;D. Gurnett;D. Kirchner;R. Huff;R. Orosei;A. Safaeinili;J. Plaut;G. Picardi
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文献类型：
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作者：
E. Nielsen;X.‐D. Wang;D. Gurnett;D. Kirchner;R. Huff;R. Orosei;A. Safaeinili;J. Plaut;G. Picardi
[1] 火星快车号航天器上的低频雷达——火星地下及电离层探测先进雷达（MARSIS），被用于探测火星电离层顶部的电子密度。该雷达记录反射无线电波回波的延迟时间随频率的变化，从而产生带有雷达回波轨迹的频谱图。有时，在火星电离层的频谱图中会出现两条轨迹。其中一条轨迹对应于来自天底方向的反射，另一条轨迹则源于电离层中的一个局部反射体。这些局部反射体可能与近垂直地壳磁场的尖状区域有关。反射的视天底角偶尔会增大到90°。这表明火星电离层中存在电子等密度高度的陡峭梯度，并显示火星等离子体垂直扩散的水平空间快速变化。这种梯度可能是由于太阳风优先进入尖状区域，或者是由于来自电离层上方尖状磁场线上加速区域的高能电子沉降而产生的。
[1] The low-frequency radar, Mars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS), on board the Mars Express spacecraft is used to sound electron densities in the topside Martian ionosphere. The radar records the delay times to echoes of reflected radio waves as a function of frequency, yielding spectrograms with traces of radar echoes. At times, two traces are present in spectrograms of the Martian ionosphere. One of these traces corresponds to reflections from the direction to nadir. The other trace originates in a localized reflector in the ionosphere. The local reflectors can be associated with the cusplike regions of near-vertical crustal magnetic fields. The apparent nadir angle of reflection can occasionally increase to 90°. This suggests that steep gradients of the altitude of the electron isodensity exist in the Martian ionosphere and indicates rapid horizontal spatial variations of vertical diffusion of Martian plasma. Such gradients may arise owing to preferential access of solar wind to the cusplike regions or to precipitation of energetic electrons from acceleration regions located on cusp magnetic field lines high above the ionosphere.