模拟太阳黑子大气中的时距模式
Time-Distance Modelling In A Simulated Sunspot Atmosphere
摘要：
与时距测量有关的主要不确定性之一是如何解释在强磁场区域进行的观测，因为将磁场的影响与热或声速扰动隔离开来已证明是相当复杂的。解耦这些效应的一种可能方法是使用3D太阳黑子模型，周围分层，安静的太阳大气来模拟磁声射线传播，并分析所产生的射线走时扰动，这将直接解释磁场。这些人工走时扰动剖面为我们提供了几个相关但不同的观测结果：i）强表面磁场对日震射线有双重影响--增加了它们的跳跃距离，同时与它们的平静太阳对应物相比大大加快了它们的速度，ii）在模拟的太阳黑子半径上，跳跃距离和旅行时间扰动都有明显的频率依赖性，iii）这些扰动的负号和大小似乎与太阳黑子的磁场强度和倾角直接相关，iv）通过“关闭”太阳黑子内部的磁场，我们能够完全隔离观测到的旅行时间扰动的热分量，可以看出，其符号与存在磁场时所测量的符号相反，并且幅度小得多。这些结果往往表明，纯粹的热扰动是不可能的主要影响，通过太阳黑子的旅行时间和强大的，近地表磁场可能会直接和显着改变的幅度和横向范围的声速反演太阳黑子的时间距离日震学。
英文摘要：
One of the main uncertainties associated with time-distance measurements is how to interpret observations made in regions of strong magnetic field as isolating the effects of the magnetic field from thermal or sound-speed perturbations has proved to be quite complex. One possible way to decouple these effects is by using a 3D sunspot model, with a surrounding stratified, quiet-Sun atmosphere to model the magneto-acoustic ray propagation, and analyze the resulting ray travel-time perturbations that will directly account for the magnetic field. These artificial travel-time perturbation profiles have provided us with several related but distinct observations: i) that strong surface magnetic fields have a dual effect on helioseismic rays -- increasing their skip distance while at the same time speeding them up considerably compared to their quiet-Sun counterparts, ii) there is a clear and significant frequency dependence of both skip-distance and travel-time perturbations across the simulated sunspot radius, iii) the negative sign and magnitude of these perturbations appears to be directly related to the sunspot magnetic-field strength and inclination, iv) by ``switching off'' the magnetic field inside the sunspot, we are able to completely isolate the thermal component of the travel-time perturbations observed, which is seen to be both opposite in sign and much smaller in magnitude than those measured when the magnetic field is present. These results tend to suggest that purely thermal perturbations are unlikely to be the main effect seen in travel times through sunspots and that strong, near-surface magnetic fields may be directly and significantly altering the magnitude and lateral extent of sound-speed inversions of sunspots made by time-distance helioseismology.
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