Electron pitch angle distributions as indicators of magnetic field topology near Mars
Electron pitch angle distributions as indicators of magnetic field topology near Mars
复制标题
DOI：
10.1029/2007ja012435
复制
发表时间：
2007-09
影响因子：
--
通讯作者：
D. Brain;R. Lillis;D. Mitchell;J. Halekas;R. Lin
中科院分区：
文献类型：
--
作者：
D. Brain;R. Lillis;D. Mitchell;J. Halekas;R. Lin
[1]我们分析了火星附近7年来记录的电子角度分布，以限制火星附近磁力线的拓扑结构。我们利用火星全球探测器在∼400公里高度测量到的115 eV电子的6300万个俯仰角分布，并根据它们的形状对它们进行了分类。封闭的磁力线与火星地壳磁场有关，并在夜间通过等离子体空洞或两侧损失锥(俘获分布)的存在来识别。黑夜侧的俘获分布最常出现在中强地壳区域周围，这表明闭合磁场区域的外层存在重联等震源过程。开放磁力线是在地壳强磁场区域通过没有从行星返回的场排列的电子(损失锥)来识别的。在远离地壳来源的地区，许多场线与碰撞大气相交。在火星的白天，闭合的场线是通过俘获或完全各向同性分布的存在来识别的，它们发生在MGS电子能谱中电离层光电子特征明显的时候。某些区域的主导俯仰角分布形状的变异性表明，火星磁场拓扑是动态的，受外部条件控制。
[1] We have analyzed electron angular distributions recorded near Mars over a period of 7 years in order to constrain the topology of magnetic field lines near Mars. We used 63 million pitch angle distributions of 115 eV electrons measured at ∼400 km altitudes by the Mars Global Surveyor (MGS) spacecraft and classified them according to their shape. Closed magnetic field lines are associated with the Martian crustal magnetic fields and are identified on the nightside by the presence of plasma voids or two-sided loss cones (trapped distributions). Trapped distributions on the nightside are most often observed in regions surrounding moderate or strong crustal fields, indicating a source process such as reconnection populates the outer layers of closed magnetic field regions. Open magnetic field lines are identified in regions of strong crustal magnetic field by the absence of field-aligned electrons returning from the planet (loss cones). In regions far from crustal sources many field lines intersect the collisional atmosphere. On the Martian dayside, closed field lines are identified by the presence of trapped or fully isotropic distributions, and they occur at times when ionospheric photoelectron features are evident in MGS electron energy spectra. Variability of the dominant pitch angle distribution shape in certain regions suggests that Martian magnetic field topology is dynamic and is controlled by external conditions.