The three candidate models submitted by the British Geological Survey for the 13th generation International Geomagnetic Reference Field are described. These DGRF and IGRF models are derived from vector and scalar magnetic field data from the European Space Agency Swarm satellites and ground observatories, covering the period 2013.9 to 2019.7. The internal field model has time dependence for degrees 1 to 15, represented by order 6 B-splines with knots at six monthly intervals. We also solve for a degree 1 external field time dependence describing annual and semi-annual signals with additional dependence on a bespoke Vector Magnetic Disturbance index. Satellite data are weighted by spatial density, along-track standard deviations, and a larger-scale noise estimator defined in terms of a measure of Local Area Vector Activity at the geographically closest magnetic observatories to the sampled datum. Forecasting of the magnetic field secular variation for 2020–2025 is by advection of the main field using steady core surface flows with steady acceleration applied. We also investigate the performance of the previous generation of candidate secular variation models, for IGRF-12, analysing the agreement of the candidates between 2015 and 2020 with the retrospective IGRF-13. We find that there is no clear distinction between the performance of mathematically and physically extrapolated forecasts in the period 2015–2020. We confirm that the methodology for the BGS IGRF-12 predictions performed well, despite observed secular accelerations that are highlighted by our analysis, and thus justify the methodology used for our IGRF-13 SV candidate.

描述了英国地质调查局为第13代国际地磁参考场提交的三个候选模型。这些DGRF和IGRF模型是从欧洲航天局群虫卫星和地面天文台的矢量和标量磁场数据得出的，涵盖了2013.9至2019.7期间。内部场模型的时间依赖性为1到15度，由6个B样条的B阶样条以六个月的间隔打结。我们还解决了描述一年和半年度信号的1度外部场时间依赖性，以及对定制矢量电磁干扰指数的额外依赖性。卫星数据通过空间密度，沿轨标准差，以及一个较大的噪声估计器，该估计器是根据地理上最靠近采样基准的磁观测站的局部区域矢量活动量度来定义的。2020-2025年的磁场长期变化的预测是通过使用稳定磁芯表面流并施加稳定加速度对主磁场进行平流来实现的。我们还针对IGRF-12调查了上一代候选世俗变异模型的性能，分析了2015年至2020年候选者与回顾性IGRF-13的协议。我们发现，在数学推算和物理推算的预测之间的表现在2015-2020年之间没有明显区别。尽管我们的分析强调了观测到的长期加速度，但我们确认BGS IGRF-12预测的方法效果良好。