Erdélyi R, Mather J F
Solar Physics and Space Plasma Research Centre (SP2RC), School of Mathematics and Statistics, University of Sheffield, Hicks Building, Hounsfield Road, Sheffield, S3 7RH UK.
Sol Phys. 2017;292(2):26. doi: 10.1007/s11207-017-1051-1. Epub 2017 Jan 19.
Magnetoacoustic gravity (MAG) waves have been studied for some time. In this article, we investigate the effect that a shear flow at a tangential discontinuity embedded in a gravitationally stratified and magnetised plasma has on MAG surface waves. The dispersion relation found is algebraically analogous to the relation of the non-flow cases obtained by Miles and Roberts ( , 205, 1992), except for the introduction of a Doppler-shifted frequency for the eigenvalue. This feature, however, introduces rather interesting physics, including the asymmetric presence of forward- and backward-propagating surface waves. We find that increasing the equilibrium flow speed leads to a shift in the permitted regions of propagation for surface waves. For most wave number combinations this leads to the fast mode being completely removed, as well as more limited phase speed regimes for slow-mode propagation. We also find that upon increasing the flow, the phase speeds of the backward propagating waves are increased. Eventually, at high enough flow speeds, the wave's direction of propagation is reversed and is in the positive direction. However, the phase speed of the forward-propagating wave remains mainly the same. For strong enough flows we find that the Kelvin-Helmholtz instability can also occur when the forward- and backward-propagating modes couple.
磁声重力（MAG）波已经被研究了一段时间。在本文中，我们研究了嵌入引力分层和磁化等离子体中的切向不连续处的剪切流对MAG表面波的影响。所得到的色散关系在代数上类似于迈尔斯和罗伯茨（1992年，第205页）在无流情况下得到的关系，只是特征值引入了一个多普勒频移频率。然而，这一特征引入了相当有趣的物理现象，包括向前和向后传播的表面波的不对称存在。我们发现，增加平衡流速会导致表面波传播的允许区域发生偏移。对于大多数波数组合，这会导致快模被完全消除，以及慢模传播的相速度范围更有限。我们还发现，随着流速增加，向后传播波的相速度会增加。最终，在足够高的流速下，波的传播方向会反转并变为正向。然而，向前传播波的相速度基本保持不变。对于足够强的流，我们发现当向前和向后传播模式耦合时，也会发生开尔文 - 亥姆霍兹不稳定性。
