Solar energetic particle access to distant longitudes through turbulent field-line meandering
Solar energetic particle access to distant longitudes through turbulent field-line meandering
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DOI：
10.1051/0004-6361/201527801
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发表时间：
2015-08
期刊：
影响因子：
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通讯作者：
T. Laitinen;A. Kopp;F. Effenberger;S. Dalla;M. Institute;U. C. Lancashire;Preston;UK.;
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文献类型：
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作者：
T. Laitinen;A. Kopp;F. Effenberger;S. Dalla;M. Institute;U. C. Lancashire;Preston;UK.;
上下文。现有的太阳高能粒子(SEP)传播模型利用Fokker-Planck(FP)方程将行星际等离子体湍流对SEP的影响描述为扩散效应。然而，如果不使用不切实际的强交叉场扩散，FP模型无法解释观测到的SEP在平均磁场中快速进入日球层内在经度上相距甚远的区域。目标。我们研究了最近提出的SEP传播的早期非扩散阶段是否能用真实的粒子输运参数来解释广泛的SEP事件。方法：研究方法。我们使用了一种新的模型，该模型解释了SEP沿着由于等离子体湍流而弯曲的场线的传播。在SEP事件历史的早期，这种非扩散传播模式已经被证明主导了SEP的跨场传播。我们将新模型与传统方法以及SEP观测结果进行了比较。结果。利用新的模型，我们再现了观测到的SEP峰通量的纵向范围，其特征是呈高斯分布，其扩散系数为30-50，而目前的扩散理论只能用真实的扩散系数来解释11-1CRC的范围。我们的模型还再现了SEP到达遥远经度的时间，这不能用扩散模型来解释。结论。SEP在广泛的经度范围内的早期发生可以理解为行星际介质中磁力线随机行走的结果，并且需要一个SEP输运模型来恰当地描述SEP跨场传播的非扩散早期阶段。
Context. Current solar energetic particle (SEP) propagation models describe the effects of interplanetary plasma turbulence on SEPs as diffusion, using a Fokker-Planck (FP) equation. However, FP models cannot explain the observed fast access of SEPs across the average magnetic field to regions that are widely separated in longitude within the heliosphere without using unrealistically strong cross-field diffusion. Aims. We study whether the recently suggested early non-diffusive phase of SEP propagation can explain the wide SEP events with realistic particle transport parameters. Methods. We used a novel model that accounts for the SEP propagation along field lines that meander as a result of plasma turbulence. Such a non-diffusive propagation mode has been shown to dominate the SEP cross-field propagation early in the SEP event history. We compare the new model to the traditional approach, and to SEP observations. Results. Using the new model, we reproduce the observed longitudinal extent of SEP peak fluxes that are characterised by a Gaussian profile with $\sigma=30-50^\circ$, while current diffusion theory can only explain extents of 11$^\circ$ with realistic diffusion coefficients. Our model also reproduces the timing of SEP arrival at distant longitudes, which cannot be explained using the diffusion model. Conclusions. The early onset of SEPs over a wide range of longitudes can be understood as a result of the effects of magnetic field-line random walk in the interplanetary medium and requires an SEP transport model that properly describes the non-diffusive early phase of SEP cross-field propagation.