arXivDaily arXiv每日学术速递 周一至周五更新
arXiv 2111.13435astro-ph.SR
收藏

层结大气中Alfvén波的脆弱性

On the Fragility of Alfvén waves in a Stratified Atmosphere

Paul S. Cally

备注：
14 pages, 6 figures, accepted (26 Nov 2021) for publication in MNRAS
发表信息：
MNRAS 510, 1093-1105 (2022)
阅读 PDF
arXiv 页面 ↗HTML 原文 ↗

摘要：

在等温三维（3D）平面层结大气底部，发展了慢、Alfvén和快磁流体动力学波的完全渐近展开式。连同现有的收敛Frobenius级数解决方案约$z=\infty$，匹配的数值计算，照亮从下面注入的慢波和Alfvén波的命运。二维模型中的阿尔文波是2.5维的，因为波在磁场的平面中传播，但其极化在可忽略的水平方向上垂直于磁场，并且波始终保持阿尔文波。波传播平面远离磁场的垂直平面的旋转推动等离子体位移矢量远离水平，从而将其耦合到分层。结果表明，在这样的三维模型中发生了强有力的慢阿尔文耦合。研究发现，在低层大气中产生的方向平均阿尔文波通量的频率相当于或大于声学截止的约50%可以达到顶部的阿尔文通量小磁场倾角$θ$，这增加到80%或更多的$θ$。另一方面，方向平均慢波在小倾角时转换为阿尔文波的效率可达40%，但这随着$θ$和波频率的增加而急剧降低。与以前探索的快-慢和快-阿尔芬耦合一起，这提供了有价值的见解，即注入的横波可以作为阿尔芬波到达高层大气，对太阳和恒星日冕加热和太阳/恒星风加速有影响。

英文摘要：

Complete asymptotic expansions are developed for slow, Alfvén and fast magnetohydrodynamic waves at the base of an isothermal three-dimensional (3D) plane stratified atmosphere. Together with existing convergent Frobenius series solutions about $z=\infty$, matchings are numerically calculated that illuminate the fates of slow and Alfvén waves injected from below. An Alfvén wave in a two-dimensional model is 2.5D in the sense that the wave propagates in the plane of the magnetic field but its polarization is normal to it in an ignorable horizontal direction, and the wave remains an Alfvén wave throughout. The rotation of the plane of wave propagation away from the vertical plane of the magnetic field pushes the plasma displacement vector away from horizontal, thereby coupling it to stratification. It is shown that potent slow-Alfvén coupling occurs in such 3D models. It is found that about 50% of direction-averaged Alfvén wave flux generated in the low atmosphere at frequencies comparable to or greater than the acoustic cutoff can reach the top as Alfvén flux for small magnetic field inclinations $θ$, and this increases to 80% or more with increasing $θ$. On the other hand, direction-averaged slow waves can be 40% effective in converting to Alfvén waves at small inclination, but this reduces sharply with increasing $θ$ and wave frequency. Together with previously explored fast-slow and fast-Alfvén couplings, this provides valuable insights into which injected transverse waves can reach the upper atmosphere as Alfvén waves, with implications for solar and stellar coronal heating and solar/stellar wind acceleration.

机构、总结、中文摘要均由AI分析而来，可能存在错误，请以论文正文为准。

↑