用高分辨率环图分析推知近地面流场的演变
Evolution of Near-surface Flows Inferred from High-resolution Ring-diagram Analysis
摘要：
在光球层观测到的声波的环形图分析可以提供在特定时间在特定区域下的次表面流的相对鲁棒的确定。波的穿透深度与区域的大小有关，因此测量流的深度范围与空间分辨率成反比。大多数环形图分析都集中在~15°（180 μ m）或更大范围的区域，以便为反演提供合理的模式集。HMI数据分析还提供了一组规模小三倍的环配合参数。这些提供的流量估计外1%（7毫米）的太阳，非常有限的深度分辨率，但空间分辨率足以映射结构可能与带和地区的磁活动。有一些系统性的影响，从当地的日震分析的地区在不同的部分可观察的磁盘流量的确定，并不是所有的理解。在这项研究中，我们具有较高的空间分辨率的特点，这些系统的影响，使他们可以更有效地占在映射的时间和空间演变的流量。留下开放的问题的平均结构的全球纬向环流和差异旋转，我们描述了近地表流异常的时间和纬度对应的扭转振荡模式的差异旋转和类似的模式中的纬向细胞结构观察到的SDO/HMI。
英文摘要：
Ring-diagram analysis of acoustic waves observed at the photosphere can provide a relatively robust determination of the sub-surface flows at a particular time under a particular region. The depth of penetration of the waves is related to the size of the region, hence the depth extent of the measured flows is inversely proportional to the spatial resolution. Most ring-diagram analysis has focused on regions of extent ~15° (180 Mm) or more in order to provide reasonable mode sets for inversions. HMI data analysis also provides a set of ring fit parameters on a scale three times smaller. These provide flow estimates for the outer 1% (7 Mm) of the Sun only, with very limited depth resolution, but with spatial resolution adequate to map structures potentially associated with the belts and regions of magnetic activity. There are a number of systematic effects affecting the determination of flows from local helioseismic analysis of regions over different parts of the observable disk, not all well understood. In this study we characterize those systematic effects with higher spatial resolution, so that they may more effectively be accounted for in mapping temporal and spatial evolution of the flows. Leaving open the question of the mean structure of the global meridional circulation and the differential rotation, we describe the near-surface flow anomalies in time and latitude corresponding to the torsional oscillation pattern in differential rotation and analogous patterns in the meridional cell structure as observed by SDO/HMI.
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