In this study we discuss the excitation of low frequency plasma waves in the lower-middle chromosphere region of loop footpoints for the case when the plasma can be considered in a pre-flare state. It is shown, that among the known semi-empirical models of the solar atmosphere, only the VAL (F) model together with a particular set of basic plasma parameters and amplitudes of the electric and magnetic fields supports generation of low frequency wave instability. Our results show that it is possible to predict the onset of the flare process in the active region by using the interaction of kinetic Alfven and kinetic ion-acoustic waves, which are solutions of the derived dispersion equation. The VAL (F) model allows situations when the main source of the aforementioned instability can be a sub-Dreicer electric field and drift plasma movements due to the presence of spatial inhomogeneities. We also show that the generation of kinetic Alfven and kinetic ion-acoustic waves can occur both, in plasma with a purely Coulomb conductivity and in the presence of small-scale Bernstein turbulence. The excitation of the small amplitude kinetic waves due to development of low threshold instability in plasma with relatively low values of the magnetic field strength is also discussed.

中文翻译：

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在耀斑前冕环的足点产生低频动波

在这项研究中，我们讨论了在可以考虑等离子体处于预耀斑状态的情况下，环路足点的中下部色球区域中低频等离子体波的激发。结果表明，在已知的太阳大气半经验模型中，只有 VAL (F) 模型以及一组特定的基本等离子体参数和电场和磁场的振幅支持低频波不稳定性的产生。我们的结果表明，可以通过使用动力学 Alfven 和动力学离子声波的相互作用来预测活动区耀斑过程的开始，它们是导出的色散方程的解。VAL (F) 模型允许上述不稳定性的主要来源可能是亚德雷塞电场和漂移等离子体运动（由于存在空间不均匀性）的情况。我们还表明，在具有纯库仑电导率的等离子体和存在小尺度伯恩斯坦湍流的情况下，都可以产生动力学阿尔芬波和动力学离子声波。还讨论了由于在具有相对低磁场强度值的等离子体中发展低阈值不稳定性而引起的小振幅动波的激发。