太阳活动区日震结构反演结果的解释
Interpreting Helioseismic Structure Inversion Results of Solar Active Regions
摘要：
日震技术，如环形图分析，经常被用来确定太阳活动区和平静区之间的地下结构差异。通过反演区域之间的频率差获得的结果通常被解释为它们之间的声速差。这些又被用来测量两个区域之间的温度和磁场强度差异。在本文中，我们首先表明，从反演得到的“声速”差实际上是声速差和磁分量的组合。因此，反演结果与热结构没有直接关系。接下来，使用太阳模型，包括磁场，我们开发了一个公式，使用反演结果来推断活跃和安静区域之间的磁和热结构的差异。然后，我们将我们的技术应用于现有的结构反演结果为不同对活跃和安静的区域。我们发现，磁场效应在0.985R_sun以上的浅层最强，而在表层和深层（r < 0.98R_sun）的磁场效应强度成反比，即，表面磁场越强，较深层中的磁效应越小，反之亦然。我们还发现，在较深的层中的磁效应是最强的安静的区域，与事实相一致，这些基本上是最弱的磁场在表面的区域。由于安静区被选择在其同伴活动区之前或之后，因此结果可能对活动区下磁场的演化有影响。
英文摘要：
Helioseismic techniques such as ring-diagram analysis have often been used to determine the subsurface structural differences between solar active and quiet regions. Results obtained by inverting the frequency differences between the regions are usually interpreted as the sound-speed differences between them. These in turn are used as a measure of temperature and magnetic-field strength differences between the two regions. In this paper we first show that the "sound-speed" difference obtained from inversions is actually a combination of sound-speed difference and a magnetic component. Hence, the inversion result is not directly related to the thermal structure. Next, using solar models that include magnetic fields, we develop a formulation to use the inversion results to infer the differences in the magnetic and thermal structures between active and quiet regions. We then apply our technique to existing structure inversion results for different pairs of active and quiet regions. We find that the effect of magnetic fields is strongest in a shallow region above 0.985R_sun and that the strengths of magnetic-field effects at the surface and in the deeper (r < 0.98R_sun) layers are inversely related, i.e., the stronger the surface magnetic field the smaller the magnetic effects in the deeper layers, and vice versa. We also find that the magnetic effects in the deeper layers are the strongest in the quiet regions, consistent with the fact that these are basically regions with weakest magnetic fields at the surface. Because the quiet regions were selected to precede or follow their companion active regions, the results could have implications about the evolution of magnetic fields under active regions.
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