The Origin of Switchbacks in the Solar Corona: Linear Theory
The Origin of Switchbacks in the Solar Corona: Linear Theory
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DOI：
10.3847/1538-4357/abb828
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发表时间：
2020-10
期刊：
影响因子：
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通讯作者：
G. Zank;M. Nakanotani;L.-L. Zhao-L.;L. Adhikari;J. Kasper
中科院分区：
文献类型：
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作者：
G. Zank;M. Nakanotani;L.-L. Zhao-L.;L. Adhikari;J. Kasper
之字形的起源、结构和传播特性是帕克太阳探测器（PSP）对速度峰值和磁场反转的观测提出的引人注目的问题。通过假设日冕环和开放磁场之间的交换重新连接，我们表明这会导致产生向上（进入日光层）和向下复杂结构，以快磁声速（即低等离子体β日冕中的阿尔文速度）传播，可以具有任意径向磁场偏转，包括“S形”。我们推导了折返径向磁场在非均匀超音速日冕传播时的演化方程。任意初始条件的解析解用于研究从发射∼6到∼35 R ⊙ 传播的之字形的特性，其中PSP在第一次遭遇期间观察到之字形。我们提供了与示例事件的详细比较，表明磁场和等离子体解与 PSP 观测结果一致。对于简单的单峰之字形结构，模型预测单峰或双峰结构；前者对应于 PSP 观察之字形的主体或侧翼。之字形的聚集及其有时复杂的结构可能是由于在短时间内与大量开环磁力线交换重新连接而形成的多个紧密间隔的之字形的形成。我们表明，它们的进化产生了一组复杂的、聚集的之字形，其中包括具有大振幅径向磁场和速度波动的“鞘”。
The origin, structure, and propagation characteristics of a switchback are compelling questions posed by Parker Solar Probe (PSP) observations of velocity spikes and magnetic field reversals. By assuming interchange reconnection between coronal loop and open magnetic field, we show that this results in the generation of upward (into the heliosphere) and downward complex structures propagating at the fast magnetosonic speed (i.e., the Alfvén speed in the low plasma beta corona) that can have an arbitrary radial magnetic field deflection, including “S-shaped.” We derive the evolution equation for the switchback radial magnetic field as it propagates through the inhomogeneous supersonic solar corona. An analytic solution for arbitrary initial conditions is used to investigate the properties of a switchback propagating from launch ∼6 to ∼35 R ⊙ where PSP observed switchbacks during its first encounter. We provide a detailed comparison to an example event, showing that the magnetic field and plasma solutions are in accord with PSP observations. For a simple single switchback, the model predicts either a single or a double-humped structure; the former corresponding to PSP observing either the main body or the flanks of the switchback. The clustering of switchbacks and their sometimes complicated structure may be due to the formation of multiple closely spaced switchbacks created by interchange reconnection with numerous open and loop magnetic field lines over a short period. We show that their evolution yields a complex, aggregated group of switchbacks that includes “sheaths” with large-amplitude radial magnetic field and velocity fluctuations.