Group sunspot number (GSN) series constitute the longest instrumental astronomical database providing information on solar activity. It is a compilation of observations by many individual observers, and their inter-calibration has usually been performed using linear rescaling. There are multiple published series that show different long-term trends for solar activity. We aim at producing a GSN series, with a non-linear non-parametric calibration. The only underlying assumptions are that the differences between the various series are due to different acuity thresholds of the observers, and that the threshold of each observer remains constant throughout the observing period. We use a daisy chain process with backbone (BB) observers and calibrate all overlapping observers to them. The calibration of each individual observer is performed with a probability distribution function (PDF) matrix, constructed considering all daily values for the overlapping period with the BB. The calibration of the BBs is done in a similar manner. Propagation of errors is modelled with Monte Carlo simulations. The final series extends back to 1739 and includes data from 314 observers. It suggests moderate activity during the 18th and 19th century, which is significantly lower than the high level of solar activity predicted by other recent reconstructions applying linear regressions. The new series provides a robust reconstruction, based on modern and non-parametric methods, of sunspot group numbers since 1739, and it confirms the existence of the Modern grand maximum of solar activity in the second half of the 20th century.
Gustav Spörer Was Not a Perfect Observer: Failure of the Active Day Fraction Reconstruction of Sunspot Group Numbers
我们表明，有效日分数校准方法（Willamo et al. [2017]）对于Gustav Spörer的太阳黑子群观测失败。Spörer被称为“完美的观察者”，因为他的“观察阈值SS面积”被确定为等于零，这是基于观察者可以看到和报告所有面积大于SS的群体，而忽略所有较小的群体的假设。因此，根据ADF校准方法，Spörer显然可以看到并报告所有组，无论大小，并且不应该错过任何一个。这意味着一个非常直接的测试：计算Spörer和“完美观测者”典范皇家格林威治天文台（RGO）的年平均群体数量，并将它们进行比较。它们应该在合理的（非常小的）误差范围内是相同的。我们发现，他们不是，RGO一般报告45%以上的群体比Spörer，因此，ADF方法是不普遍适用的
Institute for Space-Earth Environmental Research, Nagoya University（名古屋大学地球-宇宙环境研究所）；Institute for Advanced Research, Nagoya University（名古屋大学高级研究院）；Space Physics and Operations Division, RAL Space, Science and Technology Facilities Council, Rutherford Appleton Laboratory（科学与技术设施委员会拉尔夫空间实验室空间物理与运行部门）；Nishina Centre, Riken（理化学研究所西村中心）
Improvements of the Longitudinal Magnetic Field Measurement from the Solar Magnetic Field Telescope at Huairou Solar Observing Station
在弱场近似下，Stokes $V/I$与纵向磁场呈线性关系，但在强磁场区（如太阳黑子本影区），$B_{\Vert}$常常出现饱和现象。在这项工作中，我们打算改进\textit{Solar Magnetic Field Telescope}（SMFT）在中国怀柔太阳观测站进行的磁场观测。我们提出利用Stokes $V/I$和$B_{\Vert}$之间的非线性关系来推导磁场。为了确定这种关系的形式，我们对观测到的SMFT数据和\textit{Solar Dynamics Observatory}上的\textit{Helioseismic and Magnetic Imager}提供的磁图进行了交叉校准。详细介绍了磁场的推导算法。我们发现，使用斯托克斯$V/I$和$B_{\Vert}$之间的非线性关系，使我们能够消除太阳黑子本影内的磁场饱和。所提出的技术，使人们能够提高可靠性的SMFT磁场数据，甚至早在天基仪器时代，自1987年以来。
