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

    Progress in Simulations of Solar Energetic Particles Propagation in Large-scale Structures of Interplanetary Background Solar Wind

    • 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>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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