Dynamical Coupling between Anomalous Cosmic Rays and Solar Wind in Outer Heliosphere
Dynamical Coupling between Anomalous Cosmic Rays and Solar Wind in Outer Heliosphere
复制标题
外日球层异常宇宙线与太阳风的动力耦合
DOI：
10.3847/1538-4357/ac82ed
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发表时间：
2022
期刊：
影响因子：
--
通讯作者：
Chi Wang
中科院分区：
文献类型：
--
作者：
Xiaocheng Guo;Yucheng Zhou;Vladimir Florinski;Chi Wang
旅行者2号(V2)观测到拾取离子(PUI)和反常宇宙线(ACR)对外日光层太阳风结构有重要影响。特别是，高能粒子强度的最大值往往滞后于激波前沿，而在某些情况下，流动速度在激波前方具有先驱特征。这两个效应被认为分别是由于ACR在较大的日心距离从PUI停止注入和ACR的向后扩散造成的。本文采用含时的MHD数值模拟方法，研究了大气环流与太阳风在日光层外的动力学耦合问题。使用了两种内边界条件，即合成的短期激波事件和基于OMNI数据库的数据驱动的太阳风变化的较长时间段。数值结果再现了ACR最大压力相对于激波锋面的滞后以及扩展的激波前兆。滞后的增长率与相应的扩散系数和从PUIS到ACRS的喷射效率有关。该模型也适用于终止激波，模拟结果同样表明，ACR分布中的峰值可以位于激波锋面下游一小段距离处，这表明含时扩散激波加速机制是解释ACR压力峰值与V2观测到的激波锋面之间滞后的一种候选机制。
Abstract Voyager 2 (V2) observed that pickup ions (PUIs) and anomalous cosmic rays (ACRs) have a significant influence on the solar wind structures in the outer heliosphere. In particular, the maxima in energetic particle intensities often lagged behind the shock front, while the flow velocity in some cases featured a precursor in front of the shock. These two effects are believed to be caused by the cease of ACR injection from PUIs at large heliocentric distances, and the backward diffusion of ACRs, respectively. This paper investigates the dynamical coupling between the ACRs and the solar wind in the outer heliosphere by means of a time-dependent numerical MHD simulation, in which the ACRs are treated as a massless fluid that only contributes its pressure to the system. Two types of inner boundary conditions were used, namely a synthetic short-term shock event and an extended period of data-driven solar wind variability based on the OMNI database. The lag of the ACR pressure maximum relative to the shock front, and the extended shock precursor were reproduced by the numerical results. The increase rate of the lag is related to the corresponding diffusion coefficient and the injection efficiency from PUIs to ACRs. The model was also applied to the termination shock, where simulations likewise showed that the peak in the ACR distribution can be located a short distance downstream of the shock front, indicating that the time-dependent diffusive shock acceleration mechanism is a candidate to interpret the lag between the ACR pressure peak and the shock front observed by V2.