外日球层行星际激波特性与离子加速
doi: 10.11728/cjss2026.03.2025-0192 cstr: 32142.14.cjss.2025-0192
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刘思哲 男, 1999年10月出生于湖南省醴陵市, 现为哈尔滨工业大学(深圳)空间科技学院研究生, 主要研究方向为日球层等离子体物理过程的数值模拟与观测数据分析. E-mail: 23S061014@stu.hit.edu.cn -
吴明雨 男, 1987年10月出生于安徽省舒城县, 现为哈尔滨工业大学(深圳)空间科技学院副教授, 博士生导师, 主要研究方向为行星物理、等离子体波动、粒子加热加速和磁场重联等. E-mail: wumingyu@hit.edu.cn
作者简介:
Characteristics of Outer Heliospheric Interplanetary Shocks and Ion Acceleration
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摘要: 新视野号实测数据表明, 随日心距增大拾起离子在太阳风总离子中的数密度占比逐渐上升. 研究其在行星际激波处的加速, 对理解外日球层太阳风与星际物质相互作用具有重要作用. 利用二维混合模拟对外日球层行星际准垂直激波进行参量研究. 结果表明, 在较强背景湍动下, 低阿尔芬马赫数激波($ {M}_{\mathrm{A}} $<3)仍可加速部分拾起离子, 并通过扩散激波加速形成幂律高能尾; 在相同湍动强度条件下, 高能离子通量强度随马赫数增大而增加; 拾起离子更易被激波加速并主导下游高能段能谱. 对新视野号观测事件的分析发现, 部分外日球层低马赫数激波可产生幂律高能尾, 与模拟预期一致. 此外, 部分事件中, 太阳风$ \alpha $粒子或与星际中性氢电荷交换, 从而增强He+在拾起离子截止能段附近的贡献. 研究结果定性揭示了外日球层影响离子加速的参量, 为进一步理解日球层终止激波下游异常宇宙线的起源提供了理论基础.Abstract: Interstellar neutral atoms entering the heliosphere can be ionized by solar ultraviolet radiation or charge exchange with solar wind ions, then picked up by the solar wind to form interstellar Pickup Ions (PUIs). New Horizons observations show that PUIs’ number density fraction in the solar wind increases with heliocentric distance, highlighting their importance in the outer heliosphere. In this study, we conduct a parametric study of outer heliospheric interplanetary shocks using two-dimensional hybrid simulations constrained by in-situ data. Our results reveal that, for a shock with fixed Mach number, stronger ambient turbulence enhances ion multiple shock crossings via intensified upstream wave-particle scattering, prolonging particle residence near the shock. Sufficiently strong turbulence enables even low Alfvén Mach number ($ {M}_{\mathrm{A}}<3 $) shocks to efficiently accelerate PUIs into power-law suprathermal tails by diffusive shock acceleration. For given turbulence intensity, acceleration efficiency rises with Mach number due to increased compression ratio, and PUIs are accelerated more efficiently than solar wind ions, forming prominent downstream suprathermal tails. New Horizons observations of outer heliospheric low MA shocks show downstream PUI power-law tails consistent with simulations. Additionally, solar wind alpha particle-related charge exchange may enhance He+ near the PUI cutoff energy, more pronounced in high-speed streams due to larger cross-sections. This paper provide outer heliospheric ion acceleration factors and insights into anomalous cosmic ray origins downstream of the heliospheric termination shock.
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Key words:
- Pickup ions /
- Interplanetary shocks /
- Outer heliosphere /
- Turbulence /
- Ion acceleration
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图 1 SWAP观测的典型事件下游计数率能谱
Figure 1. Downstream count rate spectrum of a typical event observed by SWAP
图 2 不同湍动强度激波下游离子速度分布函数的模拟结果对比
Figure 2. Simulated ion velocity distribution function downstream of shocks under different turbulence levels
图 4 不同湍动强度激波下游离子速度分布函数的模拟结果对比
Figure 4. Simulated results for shocks with different upstream Mach numbers Red represents SWI, blue represents PUI, and the black dashed line represents SWI+PUI
图 6 新视野号参考系下典型激波模拟的下游VDF
Figure 6. Downstream ion Velocity Distribution Function (VDF) of a typical shock in the New Horizons spacecraft frame
图 7 激波S1前后的等离子体参数 (虚线表示激波面的位置)
Figure 7. Plasma parameters upstream and downstream of shock S1 (dashed line indicates the position of the shock front) Plasma parameters upstream and downstream of shock S1
图 8 激波S1前后的离子计数率能谱(两条竖直虚线分别代表上下游PUI-H+的截止能量)
Figure 8. Ion count rate spectra upstream and downstream of shock S1(two vertical dashed lines represent the cutoff energies of upstream and downstream PUI-H+, respectively)
图 9 激波S3前后的等离子体参数 (虚线表示激波面的位置)
Figure 9. Plasma parameters upstream and downstream of shock S3 (dashed line indicates the position of the shock front)
图 10 激波S3前后的离子计数率能谱竖直虚线表示上下游SWI-He+的峰值能量
Figure 10. Ion count rate spectra upstream and downstream of shock S3(two vertical dashed lines indicate the peak energies of upstream and downstream SWI-He+, respectively)
图 11 激波S4前后的等离子体参数 (虚线表示激波面的位置))
Figure 11. Plasma parameters upstream and downstream of shock S4 (dashed line indicates the position of the shock front)
图 12 激波S4前后的离子计数率能谱(两条竖直虚线分别标明了上下游PUI-H+的截止能量)
Figure 12. Ion count rate spectra upstream and downstream of shock S4(two vertical dashed lines indicate the cutoff energies of PUI-H+ in the upstream and downstream regions, respectively)
表 1 算例参数
Table 1. Simulation parameters
算例序号 湍动强度$ \varepsilon $ 上游阿尔芬马赫数$ {M}_{\mathrm{A}} $
(模拟参考系)1 0.00 10.00 2 0.25 10.00 3 0.50 10.00 4 0.50 1.50 5 0.50 2.75 
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表 2 典型事件参数表
Table 2. Parameters of typical events
激波序号 位置 太阳风速度/
(km·s–1)SWI-$ {\mathrm{H}}^{+} $
密度(×10–3)/cm–3PUI-$ {\mathrm{H}}^{+} $
密度(×10–4)/cm–3PUI-$ {\mathrm{H}}^{+} $
温度(×106)/
K磁场强度/
$ \text{nT} $压缩率$ {r}_{\mathrm{c}} $ 激波速度/
(km·s–1)上游阿尔芬马
赫数S1 上游 384.0 4.12 4.24 4.05 0.12 1.52 505.6 3.35 下游 425.6 4.56 6.43 5.78 0.18 S2 上游 364.5 10.14 7.36 3.85 0.11 1.52 463.0 4.59 下游 398.2 10.15 11.16 4.96 0.17 S3 上游 378.2 11.24 6.75 4.58 0.13 1.65 470.6 3.82 下游 414.6 11.15 11.19 5.37 0.21 S4 上游 389.4 2.69 4.63 3.91 0.12 1.92 519.5 2.98 下游 451.7 6.63 8.21 6.33 0.23 S5 上游 343.2 15.53 10.70 3.33 0.20 1.54 431.6 2.80 下游 374.2 26.62 16.44 3.74 0.31 S6 上游 373.3 14.82 8.09 3.22 0.13 2.94 486.2 5.34 下游 447.8 20.71 23.32 5.42 0.38
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