太阳高能粒子在行星际背景太阳风大尺度结构中的传播模拟进展
doi: 10.11728/cjss2025.05.2025-yg05 cstr: 32142.14.cjss.2025-yg05
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沈芳 女, 1977年12月出生于河北省怀来县, 现为中国科学院国家空间科学中心研究员, 博士生导师, 主要研究方向为灾害性空间天气事件, 包括日冕物质抛射(CME)、太阳高能粒子(SEP)传播过程数值建模等. E-mail: fshen@spaceweather.ac.cn
作者简介:
Progress in Simulations of Solar Energetic Particles Propagation in Large-scale Structures of Interplanetary Background Solar Wind
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摘要: 太阳高能粒子事件(SEP)由太阳耀斑或日冕物质抛射(CME)驱动, 能够短时间内产生几 keV 至几 GeV 能量的粒子, 其传播特性受太阳风大尺度结构显著影响, 威胁航天活动, 是空间天气预报的重点. 本文分析采用多种背景太阳风模型结合聚焦传输方程对太阳高能粒子事件的模拟, 进行细致的参数化研究, 并结合观测数据模拟多个流相互作用区(SIR)相关的SEP事件. 研究发现, 磁聚焦效应是粒子通量增强的主要原因, 快太阳风下绝热冷却效应主导通量衰减阶段演化. 太阳风参数影响共转相互作用区 (CIR) 的宽度, 导致粒子传播时空分布差异, 引入垂直扩散可解释多卫星观测的通量剖面差异. 研究构建了大尺度太阳风调制SEP传播的理论框架, 未来需融合观测数据强化CME驱动激波模拟, 以提升粒子传输预测精度.Abstract: This comprehensive review synthesizes pivotal advances in simulating Solar Energetic Particle (SEP) propagation through large-scale solar wind structures, integrating three complementary methodologies: analytical Parker-like magnetic fields for steady-state backgrounds, data-driven frameworks assimilating multi-satellite observations (STEREO, WIND) to reconstruct 2D Stream Interaction Regions (SIRs), and 3D Magnetohydrodynamic (MHD) simulations resolving tilted-dipole Corotating Interaction Regions (CIRs) with about 35° inclinations. The work quantifies how solar wind topology governs SEP dynamics, revealing that magnetic focusing dominates flux enhancements in compression zones by trapping particles in mirror-like structures, enabling multi-reflection acceleration without shocks and amplifying peak fluxes by up to 200% in simulated CIRs, while adiabatic cooling primarily drives flux decay in fast solar wind streams, with pitch-angle diffusion modulating intensity levels without altering temporal profiles. Critically, vertical diffusion reconciles multi-satellite discrepancies through cross-field transport, smoothing flux evolution as validated in the 2016 STA event (simulations matched observations within 10% error when α = 0.018～0.025), and CIR geometry—controlled by solar wind speed contrasts (ΔV>500ΔV>500 km·s–1 widening compression regions), dipole tilt angles optimizing latitudinal spread, and fast-stream widths modulating longitudinal confinement—dictates acceleration efficiency, where reverse compressions accelerate 0.5～5 MeV protons twice as effectively as forward zones due to steeper magnetic gradients. Event validations confirm these mechanisms: STEREO-A’s August 2016 CIR showed magnetic trapping explained 95% of flux rise, and STEREO-B’s September 2007 anomalous proton enhancement arose from shorter magnetic pathlengths to compression sources. Computationally, the framework synergizes focused transport equations with Stochastic Differential Equations (SDEs), where backward SDEs efficiently map observational points to source distributions and forward SDEs visualize system-wide transport, achieving a 100-fold acceleration over finite-difference methods. Future work targets transient structures (e.g., embedding CME-driven shocks via EUHFORIA/iPATH coupling) and kinetic-scale turbulence, with next-phase efforts developing unified acceleration-transport models incorporating stochastic re-acceleration, leveraging Parker Solar Probe and Solar Orbiter data to resolve magnetic islands/current sheets, and deploying machine learning to optimize background parameterization for real-time space weather forecasting.
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图 1 2016年7月31日至8月26日STA探测器在1 AU处观测的太阳风多参数与背景模型对比时序.蓝色阴影区表示研究所关注的共转相互作用区(CIR)结构[12]
Figure 1. Time-series plot comparing multiple solar wind parameters observed by the STA probe at 1 AU from July 31 to August 26, 2016, with background models. The blue shaded regions indicate the Co-rotating Interaction Region (CIR ) structures of interest in this study[12]
图 5 5 MeV的质子传播磁聚焦和投掷角扩散对通量增强的影响. (a) 通过改变由 $ {L}_{B}^{-1} $变化描述的磁聚焦效应强度得到的结果. (b) 通过设置不同的λ0值得到的投掷角扩散的影响. (c)～(f) $ \mathrm{l}\mathrm{g}\left[{G}\right({{p}}_{\mathrm{e}}\left)\right] $和 $ \mathrm{l}\mathrm{g}\left[{G}\right({p}_{\mathrm{e}}\left)\right]{f}_{\mathrm{b}}/f $作为源粒子动量$ {p}_{\mathrm{e}}/p $和观测时间函数的等高线[12]
Figure 5. Effects of magnetic focusing and pitch-angle scattering on the flux enhancement of 5 MeV proton propagation. (a) Results obtained by altering the strength of the magnetic focusing effect described by the variation of $ {L}_{B}^{-1} $. (b) Effect of pitch - angle diffusion by setting different values of λ0. (c)～(f) Contour plots of $ \mathrm{l}\mathrm{g}\left[{G}\right({{p}}_{\mathrm{e}}\left)\right] $and $ \mathrm{l}\mathrm{g}\left[{G}\right({p}_{\mathrm{e}}\left)\right]{f}_{\mathrm{b}}/f $ as functions of source particle momentum $ {p}_{\mathrm{e}}/p $ and observation time[12]
图 9 源粒子径向分布与平均积分强度的时变演化[13] (P1, P2, P3虚线分别依次对应高能粒子事件的上升、峰值和下降阶段)
Figure 9. Temporal evolution of the radial distribution and average integrated intensity of source particles[13] (The dashed lines P1, P2, and P3 correspond sequentially to the rise, peak, and decline phases of the high-energy particle event)
图 11 不同太阳风参数对粒子通量的影响. (a)在未压缩太阳风条件下, 具有两个不同背景场和太阳风参数的全向通量; (b)在压缩区域, 具有两个不同背景场和太阳风参数的全方位通量[16]
Figure 11. Impact of different solar wind parameters on particle omnidirectional fluxes. (a) Omnidirectional flux with two different background field and solar wind parameters under uncompressed solar wind conditions. (b) Omnidirectional flux with two different background field and solar wind parameters in the compression region[16]
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