纵向不均匀冕环的扭转振荡
Torsional oscillations of longitudinally inhomogeneous coronal loops
摘要：
我们探讨了一个不均匀的质量密度场的扭转阿尔芬振荡的频率和波形的太阳日冕环的影响。在弱不均匀性和强不均匀性的限制下，解析推导出扭转振动的色散关系。这些分析结果得到了数值解的验证，这些数值解对大范围的非均匀强度都是有效的。结果表明，不均匀的质量密度场导致扭转振荡的波频率的减少，相比，估计从质量密度在环顶点。这种频率的降低是由于平均阿尔芬速度的降低，只要非均匀环在其足点处更密集。导出的色散关系和波形是重要的扭转振荡，导致周期性变化的谱线宽度的潜在观测。扭转振荡为日冕地震学的发展提供了另一个强有力的工具。
英文摘要：
We explore the effect of an inhomogeneous mass density field on frequencies and wave profiles of torsional Alfven oscillations in solar coronal loops. Dispersion relations for torsional oscillations are derived analytically in limits of weak and strong inhomogeneities. These analytical results are verified by numerical solutions, which are valid for a wide range of inhomogeneity strength. It is shown that the inhomogeneous mass density field leads to the reduction of a wave frequency of torsional oscillations, in comparison to that of estimated from mass density at the loop apex. This frequency reduction results from the decrease of an average Alfven speed as far as the inhomogeneous loop is denser at its footpoints. The derived dispersion relations and wave profiles are important for potential observations of torsional oscillations which result in periodic variations of spectral line widths. Torsional oscillations offer an additional powerful tool for a development of coronal seismology.
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