Hall-coupling of Slow and Alfvén Waves at Low Frequencies in the Lower Solar Atmosphere
Hall-coupling of Slow and Alfvén Waves at Low Frequencies in the Lower Solar Atmosphere
复制标题
太阳低层大气中低频慢波和阿尔文波的霍尔耦合
作者：
Abbas Raboonik;P. Cally
在较低的太阳大气中，由于弱电离引起的霍尔效应被证明在慢磁声和Alfvén波之间产生显著的耦合，特别是在强倾斜磁场中，甚至在低频率下(≈5DocumentClass[12pt]{Minimum}usepackage{amsath}usepackage{wa ysym}usepackage{amsFonts}usepackage{amssymb}ussackage{amsbsy}usepackage{matrssfs}usepackage{upgreek}setlong{oddsidemarin}{-69pt}例如在{Document}${Approx}，5$end{Document}MHz及以上)。基于二维等温模式大气中磁声线性波解的精确解，采用微扰方法计算了三维极化Alfvén波的耦合。首先，根据磁场倾角、频率和波数的不同，快波在底部被注入，并在Alfvén声学均分高度被部分且经常强烈地反射/转换为下行慢波。然后，这个慢波通过霍尔效应强烈耦合到下行的阿尔芬波，以获得逼真的霍尔参数。与场倾角相反的水平波数和100G附近的磁场耦合最强，在这些磁场中，霍尔参数的大值与慢波和阿尔芬波的波形几乎相同的区域是共空间的。其次，在底部注入一个慢波，发现在波数-频率平面的某些区域，声波-重力波消失的地方，慢波与上行的阿尔芬波耦合得更强烈。这些结果与霍尔介导的快速阿尔芬耦合的结果相反，后者在大气中发生得更高，并且只有在更高的频率下才明显。
The Hall effect due to weak ionization in the lower solar atmosphere is shown to produce significant coupling between slow magneto-acoustic and Alfvén waves, especially in highly inclined magnetic fields, and even at low frequencies (≈5documentclass[12pt]{minimal} usepackage{amsmath} usepackage{wasysym} usepackage{amsfonts} usepackage{amssymb} usepackage{amsbsy} usepackage{mathrsfs} usepackage{upgreek} setlength{oddsidemargin}{-69pt} egin{document}${approx }, 5$end{document} mHz and above). Based on the exact magneto-acoustic linear wave solutions in a 2D isothermal model atmosphere, a perturbation approach is used to calculate the coupling to Alfvén waves polarized in the third dimension. First, a fast wave is injected at the bottom and is partially and often strongly reflected/converted to a down-going slow wave at the Alfvén-acoustic equipartition height, depending on magnetic field inclination, frequency, and wave number. This slow wave then couples strongly to the down-going Alfvén wave via the Hall effect for realistic Hall parameters. The coupling is strongest for horizontal wavenumbers oriented opposite to the field inclination, and magnetic fields around 100 G, for which large values of the Hall parameter are co-spatial with the region where slow and Alfvén waves have almost identical wave forms. Second, a slow wave is injected at the bottom, and found to couple even more strongly to up-going Alfvén waves in certain regions of the wavenumber–frequency plane where acoustic-gravity waves are evanescent. These results contrast with those for Hall-mediated fast-Alfvén coupling, which occurs higher in the atmosphere and is evident only at much higher frequencies.