Kinetic Simulations of Electron Acceleration by Dispersive Scale Alfven Waves in Jupiter's Magnetosphere
Kinetic Simulations of Electron Acceleration by Dispersive Scale Alfven Waves in Jupiter's Magnetosphere
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DOI：
10.1029/2018gl081219
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发表时间：
2019-03-28
影响因子：
5.2
通讯作者：
Johnson, J. R.
中科院分区：
文献类型：
--
作者：
Damiano, P. A.;Delamere, P. A.;Johnson, J. R.
利用陀螺流体-动力学-电子模型研究了木星上色散尺度阿尔芬波对电子的加速作用。具体来说，模拟考虑了从木卫一等离子体环中心到高纬度地区的阿尔芬波扰动的传播，这与朱诺号卫星最近的观测结果一致（例如，Allegrini等人，2017年，https://doi.org/10.1002/2017GL073180； Mauk等人，2017a, https://doi.org/10.1038/nature23648； Mauk等人，2017b, https://doi.org/10.1002/2016GL072286； Szalay等人，2018年，https://doi.org/10.1029/2018JE005752）。在这些观测中，被激发的电子能谱本质上是宽带的，大部分的被激发是在高纬度的惯性阿尔芬波的相互作用下进行的。与这些波相关的能量的程度与波扰动的大小和环面与高纬度密度的比率成正比。最近对朱诺号卫星在木星上的观测表明，高纬度地区的电子能谱是宽频的，也就是说，能量范围从几十电子伏特到几十、几百电子伏特不等。在地球上，这样的电子能谱与阿尔芬波的电子能量有关，阿尔芬波是沿着磁场线传播的横波，与弦上的波非常相似。特别是，在小尺度下（例如，围绕电场线的离子轨道的垂直尺度长度），动力学效应允许产生显著的电场，可以有效地加速平行于电场线的电子。在这种尺度上，这种波被称为色散阿尔芬波。在这项工作中，我们首次提出了木星电子能量的全球尺度（整个偶极场线）动力学模拟。我们说明了这些色散Alfven波，来源于木卫一等离子体环面，导致靠近木星电离层的宽带电子能量，这与朱诺号的观测结果在质量上是一致的。我们还说明了木卫一等离子体环面（这是木星电离层特有的特征）的存在如何影响这种宽带通电的特性。
Electron acceleration by dispersive scale Alfven waves at Jupiter is investigated using a Gyrofluid-Kinetic-Electron model. Specifically, the simulations consider the propagation of an Alfven wave perturbation from the center of the Io plasma torus to high-latitude regions that are consistent with recent Juno satellite observations (e.g., Allegrini et al., 2017, https://doi.org/10.1002/2017GL073180; Mauk, et al., 2017a, https://doi.org/10.1038/nature23648; Mauk, et al., 2017b, https://doi.org/10.1002/2016GL072286; Szalay et al., 2018, https://doi.org/10.1029/2018JE005752). As in those observations, the energized electron spectra is broadband in nature and the majority of the energization is under the interaction of inertial Alfven waves at high latitudes. The extent of the energization associated with these waves is proportional to both the magnitude of the wave perturbation and the ratio of the torus to high-latitude density.Plain Language Summary Recent observations of the Juno satellite at Jupiter illustrate that the electron energy spectrum at high latitudes is observed to be broadband-that is, ranging in energies from tens of electron volts to tens and hundreds of kiloelectron volts. At Earth, such electron spectra are associated with electron energization by Alfven waves-which are transverse waves that travel along magnetic field lines in close analogy to waves on a string. In particular, at small scales (e.g., perpendicular scale lengths on the order of the ion orbit around the field line), kinetic effects allow for significant electric field generation that can efficiently accelerate electrons parallel to the field line. At these scales, the waves are known as dispersive Alfven waves. In this work, we, for the first time, present global-scale (entire dipolar field line) kinetic simulations of electron energization at Jupiter. We illustrate that these dispersive Alfven waves, sourced in the Io plasma torus, lead to broadband electron energization close to the Jupiter ionosphere that is qualitatively consistent with the Juno observations. We additionally illustrate how the presence of the Io plasma torus (which is a feature unique to the Jupiter ionosphere) affects the characteristics of this broadband energization.