Structural Invariance of Sunspot Umbrae over the Solar Cycle: 1993 – 2004
Structural Invariance of Sunspot Umbrae over the Solar Cycle: 1993 – 2004
复制标题
太阳周期中太阳黑子本影的结构不变性：1993 – 2004
DOI：
10.1007/s11207-009-9493-8
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发表时间：
2009
期刊：
影响因子：
2.8
通讯作者：
M. Penn
中科院分区：
文献类型：
--
作者：
T. Schad;M. Penn
为研究太阳活动周期中的本影结构和强度，对1993 - 2004年美国国家航空航天局/国家太阳天文台（NASA/NSO）光谱磁图上的12967个太阳黑子本影进行了最大磁通量、最小强度和大小的测量。使用自动阈值技术选择阴影。测量的本影强度首先针对中心到边缘强度依赖性进行校正。对数正态拟合所观察到的尺寸分布证实，尺寸谱形状不随时间变化。强度-磁通量的关系被发现是稳定的太阳周期。磁通量和最小强度对本影大小的依赖关系也与周期相位无关，并分别给出线性和二次关系。虽然大的样本量确实显示出与太阳周期相关的平均最小强度和最大磁通量的低振幅振荡，但这可以用平均本影大小的变化来解释。然而，这些大小变化很小，并不能证明太阳产生的本影的大小谱发生了有意义的变化。因此，与以前的报告相比，观测结果表明了平衡结构，如不变的大小-磁场关系所示，以及平均大小（即，太阳黑子本影的强度）并不显著地依赖于太阳周期阶段。
Measurements of maximum magnetic flux, minimum intensity, and size are presented for 12 967 sunspot umbrae detected on the National Aeronautics and Space Administration/National Solar Observatory (NASA/NSO) spectromagnetograms between 1993 and 2004 to study umbral structure and strength during the solar cycle. The umbrae are selected using an automated thresholding technique. Measured umbral intensities are first corrected for center-to-limb intensity dependence. Log-normal fits to the observed size distribution confirm that the size-spectrum shape does not vary with time. The intensity – magnetic-flux relationship is found to be steady over the solar cycle. The dependence of umbral size on the magnetic flux and minimum intensity are also independent of the cycle phase and give linear and quadratic relations, respectively. While the large sample size does show a low-amplitude oscillation in the mean minimum intensity and maximum magnetic flux correlated with the solar cycle, this can be explained in terms of variations in the mean umbral size. These size variations, however, are small and do not substantiate a meaningful change in the size spectrum of the umbrae generated by the Sun. Thus, in contrast to previous reports, the observations suggest the equilibrium structure, as manifested by the invariant size-magnetic field relationship, as well as the mean size (i.e., strength) of sunspot umbrae do not significantly depend on the solar-cycle phase.