Separating multi-decadal internal geomagnetic secular variation and magnetospheric field variations

磁核场及其磁层在从小时(磁暴)到数百万年(磁极反转)的时间尺度上显示出相关的变化。地磁观测的贡献来自：地球外核地球发电机过程产生的主场；磁化岩石和地质结构产生的岩石圈磁场；电离层和磁层电流系统产生的高度多变的磁场，地壳和地幔导电结构感应产生的次要磁场。区分不同的贡献对于理解潜在过程及其对未来主场演化、空间气象条件或岩石圈异常解释的影响至关重要。这种分离仍然是一个挑战。现代矢量磁场卫星数据导致了日益精确的地磁主场模型，它们共同估计了大尺度的磁层磁场。在利用地磁观测站时间序列进行内场长期变化研究时，传统上是用月或年平均值滤除外场变化及其诱发的对应场。现代模型与这类数据的比较证实，这些时间序列中存在多年至年代际磁层变化，这对于在比卫星数据更宽的频率范围内研究内部长期变化和主场演化特征至关重要。地磁活动指数如DST(扰动风暴时间)指数被用来描述磁层磁场的变化。DST指数在设计上没有正确地描述长期变化。已经提出了一些改进DST的建议，但没有一项具体涉及十年稳定性和绝对水平。该项目旨在从地磁观测站和重复站时间序列中更好地分离磁层磁场的多年至年代际变化和内部长期变化。我们将利用爱丁堡世界数据中心提供的全球地面数据汇编，以及根据CHAMP、örsted和SWORM卫星的数据建立的现代模型中分离内部和磁层磁场的结果(特别是包括在本SPP内获得的新发现)，利用地面数据编制一个新的磁层和感应对应索引，该索引可追溯到20世纪初。好处将是双重的：首先，增进对磁层长期变化的了解是重要的，例如关于空间气象的影响。其次，更干净的内部野外地面数据将能够更详细地研究十年来的长期变化和核心场特征，以更好地了解核心动力学和地球发电机过程，并将促进使用重复台站数据来利用矢量场信息来增强总场岩石圈异常图。

The magnetic core field and its magnetosphere show relevant changes on time scales from hours (magnetic storms) to millions of years (polarity reversals). Geomagnetic observations contain contributions from: the main field produced by geodynamo processes in Earth's outer core; the lithospheric field from magnetized rocks and geological structures; and highly variable fields caused by current systems in ionosphere and magnetosphere with secondary fields from induction in conductive structures in the Earth's crust and mantle. Separation of the different contributions is essential to understand the underlying processes with implications for future main field evolution, space weather conditions or interpretation of lithospheric anomalies. This separation remains a challenge. Modern vector magnetic field satellite data lead to increasingly accurate geomagnetic main-field models that co-estimate large-scale magnetospheric fields. When using geomagnetic observatory time series for internal field secular variation studies external field variations and their induced counterparts are traditionally filtered out by using monthly or annual mean values. Comparisons of the modern models to such data confirm that multi-annual to decadal magnetospheric variations are present in these time series, which are essential to investigate internal secular variation and characteristics of main field evolution on a wider frequency range than available from satellite data. Geomagnetic activity indices like the Dst (disturbed storm time) index were developed to describe magnetospheric field variations. The Dst index by design does not describe long-term variations correctly. A number of improvements to Dst have been suggested, but none of them has specifically addressed the decadal stability and absolute level. This project aims to derive a method to better separate the multi-annual to decadal magnetospheric field variations and internal secular variation from geomagnetic observatory and repeat station time series. We will take advantage of the global data compilations of ground data available from the World Data Center Edinburgh and the results from separating internal and magnetospheric fields in the modern models based on data from the satellites CHAMP, Ørsted and Swarm (in particular including new findings obtained within this SPP) to develop a new magnetospheric and induced counterpart index using ground data, that can be extended back to the early 20th century. The benefits will be twofold: Firstly, an improved understanding of long-term magnetospheric variations is important, e.g., regarding space weather implications. Secondly, cleaner internal field ground data will enable more detailed studies of decadal secular variation and core field characteristics to better understand core dynamics and geodynamo processes and will also facilitate the use of repeat station data to augment total field lithospheric anomaly mappings with vector field information.