Provornikova E, Laming J M, Lukin V S
George Mason University, Fairfax, VA, 22030, USA.
Naval Research Laboratory, Washington, DC 20375, USA.
Astrophys J. 2018 Jun 20;860(2). doi: 10.3847/1538-4357/aac1c1.
Magnetic reconnection in the solar corona is thought to be unstable with the formation of multiple interacting plasmoids, and previous studies have shown that plasmoid dynamics can trigger MHD waves of different modes propagating outward from the reconnection site. However, variations in plasma parameters and magnetic field strength in the vicinity of a coronal reconnection site may lead to wave reflection and mode conversion. In this paper we investigate the reflection and refraction of fast magnetoacoustic waves near a reconnection site. Under a justified assumption of an analytically specified Alfvén speed profile, we derive and solve analytically the full wave equation governing the propagation of fast-mode waves in a non-uniform background plasma without recourse to the small wavelength approximation. We show that the waves undergo reflection near the reconnection current sheet due to the Alfvén speed gradient and that the reflection efficiency depends on the plasma- parameter, as well as on the wave frequency. In particular, we find that waves are reflected more efficiently near reconnection sites in a low- plasma, which is typical under solar coronal conditions. Also, the reflection is larger for lower-frequency waves while high-frequency waves propagate outward from the reconnection region almost without the reflection. We discuss the implications of efficient wave reflection near magnetic reconnection sites in strongly magnetized coronal plasma for particle acceleration, and also the effect this might have on first ionization potential (FIP) fractionation by the ponderomotive force of these waves in the chromosphere.
日冕中的磁重联被认为会因多个相互作用的等离子体团的形成而不稳定，并且先前的研究表明，等离子体团动力学可以触发从重联位点向外传播的不同模式的磁流体动力学波。然而，日冕重联位点附近等离子体参数和磁场强度的变化可能会导致波的反射和模式转换。在本文中，我们研究了重联位点附近快磁声波的反射和折射。在对解析指定的阿尔文速度剖面进行合理假设的情况下，我们推导并解析求解了在非均匀背景等离子体中控制快模波传播的完整波动方程，而无需借助小波长近似。我们表明，由于阿尔文速度梯度，波在重联电流片附近会发生反射，并且反射效率取决于等离子体参数以及波的频率。特别地，我们发现在低等离子体中，波在重联位点附近的反射更有效，这在日冕条件下是典型的。此外，低频波的反射更大，而高频波几乎没有反射地从重联区域向外传播。我们讨论了在强磁化日冕等离子体中磁重联位点附近有效波反射对粒子加速的影响，以及这些波在色球层中的有质动力可能对第一电离势（FIP）分馏产生的影响。
