Preferential Energization of Lower‐Charge‐State Heavier Ions in the Near‐Earth Magnetotail
Preferential Energization of Lower‐Charge‐State Heavier Ions in the Near‐Earth Magnetotail
复制标题
近地磁尾中低电荷态重离子的优先赋能
DOI：
10.1029/2021ja029786
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发表时间：
2022
期刊：
影响因子：
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通讯作者：
Shinohara I.
中科院分区：
文献类型：
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作者：
Keika K.;Kasahara S.;Yokota S.;Hoshino M.;Seki K.;Amano T.;Kistler L. M.;Nos? M.;Miyoshi Y.;Hori T.;Shinohara I.
O+离子对磁暴期间内磁层等离子体压力有重要贡献。风暴时O+的增强主要是由电离层的增强供应和磁尾的优先供应引起的。为了表征主导磁尾过程，我们研究了不同离子种类，即H+，He++，He+之间的能量为10-180 keV/q的离子的能谱的差异。O++和O+。我们使用Arase（ERG）航天器上的MEP‐i仪器在2017年5月和7月风暴的主要和早期恢复阶段在2015 - 2017 Re的径向距离范围内进行的观测。能谱的比较表明，对于相同的电荷状态，较重的离子比较轻的离子更能激发。对于相同的质量，较低电荷态离子比较高电荷态离子更能激发。的光谱表现出急剧下降，在高能量的所有离子物种，而更多的能量离子的光谱向更高的能量，相比那些能量较低的离子。结果表明，优先的电子自旋是由于温度升高，而不是在高能尾部产生高能离子。考虑到重离子动力学运动的时间和空间尺度，我们得出的结论是，较低电荷态重离子的优先激发发生在偶极过程中，这可能是由于近地等离子体片中的非绝热加热、传输过程中的有效捕获。局部流动通道和/或近地流动制动区域内的非绝热加速。
O+ ions make a significant contribution to plasma pressure in the inner magnetosphere during magnetic storms. The storm‐time O+ enhancements are primarily caused by enhanced supply from the ionosphere and preferential energization in the magnetotail. In order to characterize the magnetotail process that dominates the energization, we examine differences in energy spectra of energetic 10–180 keV/q ions between different ion species, namely H+, He++, He+. O++, and O+. We use observations made by the MEP‐i instrument on the Arase (ERG) spacecraft on the nightside in the radial distance range of ∼5–∼7 Re during the main and early recovery phases of the May and July 2017 storms. The comparisons of energy spectra show that, for the same charge states, heavier ions are more energized than lighter ions. For the same mass, lower‐charge‐state ions are more energized than higher‐charge‐state ions. The spectra exhibit a sharp decrease at high energies for all ion species, while the spectra for more energized ions were shifted toward higher energies, compared to those for less energized ions. The results suggest that the preferential energization is due to temperature increases rather than the generation of energetic ions in the high‐energy tail. Considering temporal and spatial scales of heavy ion kinetic motions, we conclude that the preferential energization of lower‐charge‐state heavier ions occurs during the course of dipolarization, likely due to non‐adiabatic heating in the near‐Earth plasma sheet, effective trapping during transport by localized flow channels, and/or non‐adiabatic acceleration within the near‐Earth flow‐braking region.