THE BEHAVIOR OF TRANSVERSE WAVES IN NONUNIFORM SOLAR FLUX TUBES. II. IMPLICATIONS FOR CORONAL LOOP SEISMOLOGY
THE BEHAVIOR OF TRANSVERSE WAVES IN NONUNIFORM SOLAR FLUX TUBES. II. IMPLICATIONS FOR CORONAL LOOP SEISMOLOGY
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DOI：
10.1088/0004-637x/781/2/111
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发表时间：
2013-12
期刊：
影响因子：
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通讯作者：
R. Soler;M. Goossens;J. Terradas;R. Oliver
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作者：
R. Soler;M. Goossens;J. Terradas;R. Oliver
利用阻尼横向振荡观测结合理论模型结果的日冕环地震学是间接推断太阳大气等离子体物理参数的一种工具。现有的基于扭结振荡周期和阻尼时间近似值的地震学方案经常超出其理论适用范围。这些近似假设环上密度的变化局限于比环半径薄得多的非均匀层，但反演问题的结果往往不满足这一初步假设。在这里，我们确定了周期和阻尼时间的解析近似的准确性，以及当考虑大部分非均匀环路时对地震学估计的影响。我们发现，当使用超出其适用范围时，近似值的准确性受到环上密度分布形式的强烈影响，这是观测未知的，因此必须作为理论模型的一部分任意施加。即使对于相对较薄的非均匀层，与解析近似相关的误差也可能大于50%。与实际数值反演相比，这个误差直接影响到近似地震学估计的准确性。此外，假设不同的密度剖面可以在同一事件的反演中产生地震变量的不重合区间。对环上密度变化的真实形状的无知是一个重要的误差来源，它可能会对假设一个特定密度剖面的地震推断参数的可靠性产生争议。
The seismology of coronal loops using observations of damped transverse oscillations in combination with results from theoretical models is a tool to indirectly infer physical parameters in the solar atmospheric plasma. Existing seismology schemes based on approximations of the period and damping time of kink oscillations are often used beyond their theoretical range of applicability. These approximations assume that the variation of density across the loop is confined to a nonuniform layer much thinner than the radius of the loop, but the results of the inversion problem often do not satisfy this preliminary hypothesis. Here, we determine the accuracy of the analytic approximations of the period and damping time, and the impact on seismology estimates when largely nonuniform loops are considered. We find that the accuracy of the approximations when used beyond their range of applicability is strongly affected by the form of the density profile across the loop, that is observationally unknown and so must be arbitrarily imposed as part of the theoretical model. The error associated with the analytic approximations can be larger than 50% even for relatively thin nonuniform layers. This error directly affects the accuracy of approximate seismology estimates compared to actual numerical inversions. In addition, assuming different density profiles can produce noncoincident intervals of the seismic variables in inversions of the same event. The ignorance about the true shape of density variation across the loop is an important source of error that may dispute the reliability of parameters seismically inferred assuming an ad hoc density profile.