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

在时间尺度上，从数小时（磁暴）到数百万年（极性反转），磁芯场及其磁层都表现出相关的变化。地磁观测包含以下方面的贡献：地球外核的地球发电机过程产生的主要场;磁化岩石和地质结构产生的岩石圈场;电离层和磁层电流系统产生的高度可变场，以及地壳和地幔导电结构感应产生的次级场。分离不同的贡献是必不可少的，以了解潜在的过程与未来的主要领域的演变，空间天气条件或解释岩石圈异常的影响。这种分离仍然是一个挑战。现代矢量磁场卫星数据导致越来越精确的地磁主场模型，共同估计大规模磁层场。在利用地磁观测时间序列研究内场长期变化时，通常采用月或年平均值来滤除外场变化及其引起的变化。现代模型与这些数据的比较证实，在这些时间序列中存在多年到十年的磁层变化，这对于在比卫星数据更宽的频率范围内调查内部长期变化和主要磁场演变特征至关重要。地磁活动指数，如Dst（扰动风暴时间）指数，是用来描述磁层场的变化。Dst指数的设计不能正确描述长期变化。对Dst的一些改进已经被提出，但没有一个是专门针对年代际稳定性和绝对水平的。本计画的目的是探讨一种从地磁观测站与复测站时间序列中，更好地分离出多年至十年的磁层场变化与内部长期变化的方法。我们将利用爱丁堡世界数据中心提供的地面数据的全球数据汇编，以及根据CHAMP、Crsted和Swarm卫星提供的数据在现代模型中分离内部场和磁层场的结果（特别是包括在该特别方案范围内获得的新发现）利用地面数据制定新的磁层和感应对应指数，可以追溯到世纪早期。好处有两方面：首先，必须增进对磁层长期变化的了解，例如，关于空间天气的影响。其次，更干净的内部场地面数据将使十年长期变化和核心场特征的更详细的研究，以更好地了解核心动力学和地球发电机过程，也将有利于使用重复站数据，以增加总场岩石圈异常映射与矢量场信息。

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.