We present the GFZ candidate field models for the \(13{\mathrm{th}}\) Generation International Geomagnetic Reference Field (IGRF-13). These candidates were derived from the Mag.num.IGRF13 geomagnetic core field model, which is constrained by Swarm satellite and ground observatory data from November 2013 to August 2019. Data were selected from magnetically quiet periods, and the model parameters have been obtained using an iteratively reweighted inversion scheme approximating a robust modified Huber norm as a measure of misfit. The root mean square misfit of the Mag.num.IGRF13 model to Swarm and observatory data is in the order of 3–5 nT for mid and low latitudes, with a maximum of 44 nT for the satellite east component data at high latitudes. The time-varying core field is described by order 6 splines and spherical harmonic coefficients up to degree and order 20. We note that the temporal variation of the core field component of the Mag.num.IGRF13 model is strongly damped and shows a smooth secular variation that suits well for the IGRF, where secular variation is represented as constant over 5-year intervals. Further, the external field is parameterised by a slowly varying part and a more rapidly varying part controlled by magnetic activity and interplanetary magnetic field proxies. Additionally, the Euler angles of the magnetic field sensor orientation are co-estimated. A widely discussed feature of the geomagnetic field is the South Atlantic Anomaly, a zone of weak and decreasing field strength stretching from southern Africa over to South America. The IGRF and Mag.num.IGRF13 indicate that the anomaly has developed a second, less pronounced eastern minimum at Earth’s surface since 2007. We observe that while the strong western minimum continues to drift westwards, the less pronounced eastern minimum currently drifts eastward at Earth’s surface. This does not seem to be linked to any eastward motion at the core–mantle boundary, but rather to intensity changes of westward drifting flux patches contributing to the observed surface field. Also, we report a sudden change in the secular variation measured at two South Atlantic observatories around 2015.0, which occurred shortly after the well-known jerk of 2014.0.

我们介绍了\（13 {\ mathrm {th}} \）世代国际地磁参考场（IGRF-13）的GFZ候选场模型。这些候选数据来自Magnum.IGRF13地磁核心场模型，该模型受Swarm卫星和地面观测站数据从2013年11月至2019年8月的约束。数据是从磁静周期中选择的，并且使用迭代重加权反演方案，将稳健的修改过的Huber范数近似为失配的度量。的的均方根失配Mag.num.IGRF13Swarm和天文台数据的模型在中低纬度时约为3-5 nT，在高纬度时，卫星东部分量数据的最大值为44 nT。时变核心场由阶数为6的样条和高达20阶数的球谐系数描述。我们注意到，Magnum IGRF13核心场分量的时间变化该模型被强烈阻尼，并显示出很适合IGRF的平稳的长期变化，其中长期变化表示为5年间隔内不变。此外，外部磁场由受磁活动和行星际磁场代理控制的缓慢变化的部分和更快变化的部分来参数化。另外，磁场传感器取向的欧拉角被共同估计。地磁场的一个被广泛讨论的特征是南大西洋异常，这是一个从南部非洲一直延伸到南美的弱且强度递减的区域。IGRF和Magnum.IGRF13这表明该异常现象自2007年以来在地球表面形成了第二个不那么明显的东部最小值。我们观察到，虽然强的西部最小值继续向西漂移，但较不明显的东部最小值目前在地球表面向东漂移。这似乎与岩心-地幔边界上的任何东移无关，而与向西漂移的通量斑块的强度变化有关，这有助于观测到的表面场。此外，我们报告了在2015.0左右在南大西洋的两个观测站测得的长期变化的突然变化，该变化在发生于2014.0的著名地震之后不久发生。