Electron dynamics in small magnetospheres
Electron dynamics in small magnetospheres
复制标题
小磁层中的电子动力学
DOI：
10.1051/0004-6361/202243911
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发表时间：
2022
影响因子：
6.5
通讯作者：
Benkhoff Johannes
中科院分区：
文献类型：
--
作者：
Lavorenti Federico;Henri Pierre;Califano Francesco;Deca Jan;Aizawa Sae;Andre Nicolas;Benkhoff Johannes
背景水星有一个很小但高度动态的磁层，其中电子的作用和动力学在很大程度上还不清楚。目的我们的目标是模拟太阳风电子撞击水星磁层的全球动力学。这项工作的目标是通过模拟太阳风与赫平均数磁层相互作用的三维、全动力学的粒子单元模拟来实现的。这种方法允许自洽地表示从大行星尺度到电子动力学尺度的等离子体动力学。结果发现在磁层边界(弓形激波和磁层顶)处流动着以电子为主的强等离子体电流(μAm−2量级)。这种电流是由我们模型中解析的小尺度电子物理驱动的。此外，当行星际磁场向南时，我们观察到了由于磁重联而产生的高达数十keV的电子加速。这些高能电子部分被困在行星的偶极磁场中，主要是在夜间。最后，通过研究我们的模拟中沿Marine10号和比普科伦坡第一水星掠过轨迹的电子分布，我们认为这两个航天器都在最近的接近处观察到了这个高能的准陷阱电子布居。
ContextThe planet Mercury possesses a small but highly dynamic magnetosphere in which the role and dynamics of electrons are still largely unknown.AimsWe aim to model the global dynamics of solar-wind electrons impinging on Mercury’s magnetosphere. Particular relevance is given to local acceleration processes and the global circulation patterns.MethodsThe goals of this work are pursued by means of three-dimensional, fully kinetic particle-in-cell simulations modeling the interaction of the solar wind with the Hermean magnetosphere. This method allows a self-consistent representation of the plasma dynamics from the large planetary scale down to the electron kinetic scale. We carried out numerical simulations using two different solar-wind conditions: purely northward or purely southward interplanetary magnetic field direction.ResultsWe find a high plasma current (of the order of few μA m−2) flowing at the magnetospheric boundaries (bow shock and magnetopause) dominated by electrons. This current is driven by the small-scale electron physics resolved in our model. Furthermore, we observe strong electron acceleration up to tens of keV as a consequence of magnetic reconnection when the interplanetary magnetic field is directed southward. Such energetic electrons are partially trapped in the dipolar magnetic field of the planet mainly at nightside. Finally, by studying the distribution of electrons in our simulations along Mariner10 and BepiColombo first-Mercury-flyby trajectories, we propose that both spacecraft observed this energetic quasi-trapped electron population around closest approach.