Historic geomagnetic activity observations have been used to reveal centennial variations in the open solar flux and the near-Earth heliospheric conditions (the interplanetary magnetic field and the solar wind speed). The various methods are in very good agreement for the past 135 years when there were sufficient reliable magnetic observatories in operation to eliminate problems due to site-specific errors and calibration drifts. This review underlines the physical principles that allow these reconstructions to be made, as well as the details of the various algorithms employed and the results obtained. Discussion is included of: the importance of the averaging timescale; the key differences between “range” and “interdiurnal variability” geomagnetic data; the need to distinguish source field sector structure from heliospherically-imposed field structure; the importance of ensuring that regressions used are statistically robust; and uncertainty analysis. The reconstructions are exceedingly useful as they provide calibration between the in-situ spacecraft measurements from the past five decades and the millennial records of heliospheric behaviour deduced from measured abundances of cosmogenic radionuclides found in terrestrial reservoirs. Continuity of open solar flux, using sunspot number to quantify the emergence rate, is the basis of a number of models that have been very successful in reproducing the variation derived from geomagnetic activity. These models allow us to extend the reconstructions back to before the development of the magnetometer and to cover the Maunder minimum. Allied to the radionuclide data, the models are revealing much about how the Sun and heliosphere behaved outside of grand solar maxima and are providing a means of predicting how solar activity is likely to evolve now that the recent grand maximum (that had prevailed throughout the space age) has come to an end.

中文翻译：

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太阳空磁通量和行星际条件变化的重构和预测

历史地磁活动观测已被用来揭示开放太阳通量和近地太阳圈条件（行星际磁场和太阳风速）的百年变化。在过去的135年中，当有足够的可靠磁观测站运行时，各种方法非常吻合，可以消除因特定地点的误差和校准偏差而引起的问题。这篇综述强调了允许进行这些重构的物理原理，以及所采用的各种算法的细节和所获得的结果。讨论内容包括：平均时间表的重要性；“范围”和“昼间变化”地磁数据之间的主要区别；有必要将源场扇区结构与日球施加的场结构区分开来；确保所使用的回归在统计上可靠的重要性；和不确定性分析。重建工作非常有用，因为它们可以在过去五十年的实地航天器测量结果与从在地面水库中发现的大量成因放射性核素的实测丰度推导出的千禧年行为的千禧年记录之间进行校准。使用太阳黑子数来量化出现率的开放太阳通量的连续性是许多模型的基础，这些模型非常成功地再现了由地磁活动引起的变化。这些模型使我们可以将构造扩展回磁力计开发之前的范围，并涵盖Maunder最小值。