Electron densities in the upper ionosphere of Mars from the excitation of electron plasma oscillations
Electron densities in the upper ionosphere of Mars from the excitation of electron plasma oscillations
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DOI：
10.1029/2008ja013073
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发表时间：
2008-07
影响因子：
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通讯作者：
F. Duru;D. Gurnett;D. Morgan;R. Modolo;A. Nagy;D. Najib
中科院分区：
文献类型：
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作者：
F. Duru;D. Gurnett;D. Morgan;R. Modolo;A. Nagy;D. Najib
除了对火星电离层进行远程无线电探测外，火星快车号航天器上的MARSIS（火星地下和电离层探测先进雷达）仪器也能够通过激发局部电子等离子体振荡来测量原位电子密度。本文根据这些振荡的频率对火星电离层上层的电子密度进行了研究。这种方法的优点是可以在比远程无线电探测高得多的高度测量电子密度。利用这一技术分析了2005年8月4日至2007年7月31日期间503个轨道的电子密度，高度从275公里到1300公里不等。虽然轨道之间存在相当大的差异，但在给定的太阳天顶角（SZA）下，火星白天侧的中位电子密度随着高度的增加而系统地降低，其特征等离子体尺度高度从大约80到145公里不等。在固定高度下，小于约80°的SZAs的电子密度几乎保持不变。对于大于约80°的SZA，电子密度随SZA的增加而迅速下降，在夜侧接近非常低的值。利用磁流体力学和混合代码进行的模拟表明，在给定的高度上，等离子体的密度几乎是恒定的，这是由于与太阳风的相互作用，等离子体从白天侧向夜晚侧的水平传输造成的。
[1] In addition to remote radio sounding of the ionosphere of Mars, the MARSIS (Mars Advanced Radar for Subsurface and Ionospheric Sounding) instrument on the Mars Express spacecraft is also able to measure the in situ electron density from the excitation of local electron plasma oscillations. This paper presents an investigation of the electron density in the upper ionosphere of Mars based on the frequency of these oscillations. The advantage of this method is that electron densities can be measured at much higher altitudes than can be determined from remote radio soundings. Using this technique electron densities from 503 orbits have been analyzed over the period from 4 August 2005 to 31 July 2007 for altitudes ranging from about 275 to 1300 km. Although there is considerable variability from orbit to orbit, the median electron density at a given solar zenith angle (SZA) on the dayside of Mars decreases systematically with increasing altitude with a characteristic plasma scale height varying from about 80 to 145 km. At a fixed altitude, the electron density remains almost constant for SZAs less than about 80°. For SZAs greater than about 80° the electron density decreases rapidly with increasing SZA, approaching very low values on the nightside. Simulations performed using both magnetohydrodynamic and hybrid codes show that the nearly constant density at a given altitude is caused by the horizontal transport of plasma from the dayside toward the nightside due to interaction with the solar wind.