磁通量管II的流动不稳定性。纵向流动
Flow instabilities of magnetic flux tubes II. Longitudinal flow
摘要：
流致不稳定性与恒星对流区磁场的储存和动力学有关，也可能与其他天体物理学背景有关。我们继续本系列第一篇论文中开始的研究，考虑沿磁通量管纵向流动的稳定性。进行了线性稳定性分析，以确定在薄磁通量管的近似框架的不稳定性的开始的标准。在非耗散的情况下，我们发现Kelvin-Helmholtz不稳定性的流速超过一个临界速度，取决于Alfv{é}n速度和内部和外部密度的比例。包含一个与相对横向速度成比例的摩擦项，导致与向后（或负能量）波有关的摩擦驱动的不稳定性。我们讨论这种不稳定性的物理性质。在分层外部介质的情况下，Kelvin-Helmholtz不稳定性和摩擦驱动的不稳定性可以设置在明显低于Alfv{é}n速度的流速。耗散效应可以激发低于Kelvin-Helmholtz和波动（Parker型）不稳定性阈值的流动驱动不稳定性。这对于恒星对流区的磁通量储存和天体物理喷流的稳定性可能是重要的。
英文摘要：
Flow-induced instabilities are relevant for the storage and dynamics of magnetic fields in stellar convection zones and possibly also in other astrophysical contexts. We continue the study started in the first paper of this series by considering the stability properties of longitudinal flows along magnetic flux tubes. A linear stability analysis was carried out to determine criteria for the onset of instability in the framework of the approximation of thin magnetic flux tubes. In the non-dissipative case, we find Kelvin-Helmholtz instability for flow velocities exceeding a critical speed that depends on the Alfv{é}n speed and on the ratio of the internal and external densities. Inclusion of a friction term proportional to the relative transverse velocity leads to a friction-driven instability connected with backward (or negative energy) waves. We discuss the physical nature of this instability. In the case of a stratified external medium, the Kelvin-Helmholtz instability and the friction-driven instability can set in for flow speeds significantly lower than the Alfv{é}n speed. Dissipative effects can excite flow-driven instability below the thresholds for the Kelvin-Helmholtz and the undulatory (Parker-type) instabilities. This may be important for magnetic flux storage in stellar convection zones and for the stability of astrophysical jets.
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