太阳风共转作用区对宇宙线的调制

Galactic cosmic rays (GCRs) are highly energetic charged particles that originate from regions outside the heliosphere (e.g., the galaxy). The heliosphere acts as an obstacle for GCRs and only the relatively high energy ions can reach the inner solar system. GCR propagation is strongly influenced by transient magnetic structures inside the heliosphere, including corotating interaction regions (CIRs) that are produced as a result of the interaction between fast and slow solar-wind streams. A typical CIR contains a stream interface that separates the two solar-wind streams, a leading forward wave propagating into the slower stream ahead, and a tailing reverse wave propagating back into the trailing high speed stream. These waves may steepen and evolve into shocks pairs by about 2 AU, and eventually interact with the neighboring CIRs forming corotating merged interaction regions (CMIRs). Observations also indicate the existence of CIMRs remnants in the heliosheath. Evidently, CIRs are quite ubiquitous in the heliosphere. ..There is now compelling observational evidence that the stream interfaces and the leading edges of CIRs are responsible for the depressions of GCRs intensity. We have the only numerical model currently in existence that simulates cosmic-ray transport through a complete self-consistently generated CIR structure. This project will build upon our earlier simulations to develop an understanding of the physics of GCR modulation by the CIRs and explain a number of challenging.observations. 1. Observations show that solar wind speed and the so-called VB factor (velocity times magnetic field) are strongly anti-correlated with the variations of GCR intensity. 2. Magnetic field does not appear to organize GCR structures, and in some cases multiple crossings of the heliospheric current sheet (HCS) are not accompanied by GCR depressions. 3. Cosmic-ray variation produced by CIR shock pairs and by merged CIRs at larger distances (beyond 1 AU) have not yet been investigated. The central goal of this proposal is to develop such an understanding through a series of numerical simulations including a physics-based turbulence transport model. We expect this work to make a decisive contribution to our knowledge of cosmic-ray modulation by the CIRs inside the heliosphere in general.

银河宇宙线（GCR）是源自日球层外（通常是银河系内）的一种高能粒子。日球层对其有屏障作用所以一般只有较高能量的粒子才能进入内日球层。GCR的传输受太阳风变化的影响，比如快慢太阳风作用形成的共转作用区（CIR）。一个典型的CIR有流界面（分隔快慢太阳风），前向波和一个后向波。这些波进一步发展能形成激波对，并最终与相邻的CIR相互作用，形成复杂结构共转合并作用区（CMIR），观测发现在日球层鞘区里也有这种结构，所以CIR及其衍生物在日球层广泛存在。已有观测证实流界面和前向波一般和GCR强度的下降关联。我们将利用一个自洽的CIR太阳风模型和宇宙线传输模型的集成模式，来研究这些问题：1. 观测显示太阳风速度和电场与GCR强度有很强的反相关性。2. 太阳风磁场并不总是能影响GCR变化，电流片的穿越与GCR的强度变化并没有太多关联。3. 在离日较远区CMIR对GCR的影响还没有有效地被评估。

GCR的传输受太阳风变化的影响,比如快慢太阳风作用形成的共转作用区(CIR)。一个典型的CIR有流界面(分隔快慢太阳风),前向波和一个后向波。这些波进一步发展能形成激波对,并最终与相邻的CIR相互作用,形成复杂结构共转合并作用区(CMIR),观测发现在日球层鞘区里也有这种结构,所以CIR及其衍生物在日球层广泛存在。已有观测证实流界面和前向波一般和GCR强度的下降关联，但CIR影响GCR强度的具体物理机制有待深入探讨。我们通过一个自洽的CIR太阳风模型和宇宙线传输模型的集成模式,研究了近地太阳风调制影响宇宙线传输的物理机制，模拟结果显示宇宙线在CIR附近的扩散效应对宇宙线的通量变化起着决定性的作用。另一方面，基于ACE飞船和地面中子计数器的观测，通过太阳活动低年的宇宙线与太阳风变化的统计研究发现，除了横向扩散效应外，宇宙线的漂移效应同样也起着重要的作用，在电流片附近倾向于积聚着宇宙线粒子；基于现有的宇宙线传输理论，我们尝试给出了定量化的证据。综合来看，扩散效应与漂移效应的综合作用决定了近地宇宙线随太阳风变化的趋势。