FAST SAUSAGE MODES IN MAGNETIC TUBES WITH CONTINUOUS TRANSVERSE PROFILES: EFFECTS OF A FINITE PLASMA BETA
FAST SAUSAGE MODES IN MAGNETIC TUBES WITH CONTINUOUS TRANSVERSE PROFILES: EFFECTS OF A FINITE PLASMA BETA
复制标题
具有连续横向轮廓的磁管中的快速香肠模式：有限等离子体 Beta 的影响
DOI：
10.3847/1538-4357/833/1/114
复制
发表时间：
2016
影响因子：
4.9
通讯作者：
Guo Ming-Zhe
中科院分区：
文献类型：
--
作者：
Chen Shao-Xia;Li Bo;Xiong Ming;Yu Hui;Guo Ming-Zhe
虽然耀斑环中的固定香肠模式经常被用来解释太阳耀斑中的准周期脉动（QPP），但尚不清楚它们如何受到连续横向结构和有限内部等离子体β的综合效应的影响（）。我们推导出控制直磁管中的线性腊肠波的通用色散关系，其中等离子体压力不可忽略，并且基本上任意形式的密度和温度不均匀性发生在任意宽度的层中。着眼于快速模式，我们发现仅对将泄漏模式与俘获模式分开的临界纵波数产生微弱影响。同样，对于俘获模和泄漏模，以横向快时间为单位的周期 P 仅较弱地依赖于 ，这与快香肠模的有效波矢量很大程度上垂直于背景磁场的事实相一致。然而，只有当长度与半径之比 L/R 比某个临界值大 ∼50% 时，才会看到阻尼时间 τ 的弱依赖性，该临界值本身相当敏感地取决于密度对比、剖面陡度以及横向结构的描述方式。在 QPP 的背景下，我们得出的结论是，只要将推导的内部阿尔文速度视为实际的最快速度，就可以将更简单的零贝塔理论应用于捕获模式。相反，当利用泄漏模式时，应考虑耀斑环路中有限贝塔造成的影响。
While standing fast sausage modes in flare loops are often invoked to interpret quasi-periodic pulsations (QPPs) in solar flares, it is unclear as to how they are influenced by the combined effects of a continuous transverse structuring and a finite internal plasma beta ( ). We derive a generic dispersion relation governing linear sausage waves in straight magnetic tubes for which plasma pressure is not negligible, and the density and temperature inhomogeneities of essentially arbitrary form take place in a layer of arbitrary width. Focusing on fast modes, we find that only weakly influences , the critical longitudinal wavenumber separating the leaky from trapped modes. Likewise, for both trapped and leaky modes, the periods P in units of the transverse fast time depend only weakly on , which is compatible with the fact that the effective wave vectors of fast sausage modes are largely perpendicular to the background magnetic field. However, a weak dependence of the damping times τ is seen only when the length-to-radius ratio L/R is ∼50% larger than some critical value , which itself rather sensitively depends on the density contrast, profile steepness, as well as on how the transverse structuring is described. In the context of QPPs, we conclude that the much simpler zero-beta theory can be employed for trapped modes, as long as one sees the deduced internal Alfvén speed as actually being the fast speed. In contrast, effects due to a finite beta in flare loops should be considered when leaky modes are exploited.