Electrons on closed field lines of lunar crustal fields in the solar wind wake
Electrons on closed field lines of lunar crustal fields in the solar wind wake
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太阳风尾流中月球地壳场闭合场线上的电子
DOI：
10.1016/j.icarus.2014.12.007
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发表时间：
2015
期刊：
影响因子：
3.2
通讯作者：
Hisayoshi Shimizu
中科院分区：
文献类型：
--
作者：
Masaki N. Nishino;Yoshifumi Saito;Hideo Tsunakawa;Futoshi Takahashi;Masaki Fujimoto;Yuki Harada;Shoichiro Yokota;Masaki Matsushima;Hidetoshi Shibuya;Hisayoshi Shimizu
月球地壳磁场等离子体特征是月球等离子体科学研究的重要内容之一。虽然最近的航天器测量揭示了太阳风与月球地壳场在白昼的相互作用，但在夜晚的地壳场周围的等离子体特征尚未得到充分研究。在这里，我们显示的证据等离子体捕获的闭合场线的月球地壳领域的太阳风尾流，使用SELENE（辉屋）等离子体和磁场数据在14-15公里的高度从月球表面。与预期的在强地壳场下形成等离子体空腔相反，在对极危机（CA）异常上方，电子通量增强，这是最强的月球地壳场之一。CA上方增强的电子通量的特征在于：（1）在较低能量范围（<150 eV）内偶尔出现双向场对准射束，以及（2）中等能量分量（150-300 eV），其具有代表地壳磁场的两个足迹之间的反弹运动的双损失锥分布。闭合场线上的低能电子可能来自月球的夜面，而闭合场线上的中能电子的供给机制尚待解决。我们还报告说，密度空腔的尾流中观察到的最强的磁场，但在其附近。
Plasma signature around crustal magnetic fields is one of the most important topics of the lunar plasma sciences. Although recent spacecraft measurements are revealing solar–wind interaction with the lunar crustal fields on the dayside, plasma signatures around crustal fields on the night side have not been fully studied yet. Here we show evidence of plasma trapping on the closed field lines of the lunar crustal fields in the solar–wind wake, using SELENE (Kaguya) plasma and magnetic field data obtained at 14–15 km altitude from the lunar surface. In contrast to expectation on plasma cavity formation at the strong crustal fields, electron flux is enhanced above Crisium Antipode (CA) anomaly which is one of the strongest lunar crustal fields. The enhanced electron fluxes above CA are characterised by (1) occasional bi-directional field-aligned beams in the lower energy range (<150 eV) and (2) a medium energy component (150–300 eV) that has a double loss-cone distribution representing bounce motion between the two footprints of the crustal magnetic fields. The low-energy electrons on the closed field lines may come from the lunar night side surface, while supply mechanism of medium-energy electrons on the closed field line remains to be solved. We also report that a density cavity in the wake is observed not above the strongest magnetic field but in its vicinity.