We present geomagnetic main field and secular variation time series, at 300 equal-area distributed locations and at 490 km altitude, derived from magnetic field measurements collected by the three Swarm satellites. These Geomagnetic Virtual Observatory (GVO) series provide a convenient means to globally monitor and analyze long-term variations of the geomagnetic field from low-Earth orbit. The series are obtained by robust fits of local Cartesian potential field models to along-track and East–West sums and differences of Swarm satellite data collected within a radius of 700 km of the GVO locations during either 1-monthly or 4-monthly time windows. We describe two GVO data products: (1) ‘Observed Field’ GVO time series, where all observed sources contribute to the estimated values, without any data selection or correction, and (2) ‘Core Field’ GVO time series, where additional data selection is carried out, then de-noising schemes and epoch-by-epoch spherical harmonic analysis are applied to reduce contamination by magnetospheric and ionospheric signals. Secular variation series are provided as annual differences of the Core Field GVOs. We present examples of the resulting Swarm GVO series, assessing their quality through comparisons with ground observatories and geomagnetic field models. In benchmark comparisons with six high-quality mid-to-low latitude ground observatories we find the secular variation of the Core Field GVO field intensities, calculated using annual differences, agrees to an rms of 1.8 nT/yr and 1.2 nT/yr for the 1-monthly and 4-monthly versions, respectively. Regular sampling in space and time, and the availability of data error estimates, makes the GVO series well suited for users wishing to perform data assimilation studies of core dynamics, or to study long-period magnetospheric and ionospheric signals and their induced counterparts. The Swarm GVO time series will be regularly updated, approximately every four months, allowing ready access to the latest secular variation data from the Swarm satellites.

我们展示了来自三个Swarm卫星收集的磁场测量结果，得出了300个等面积分布位置和490 km高度的地磁主场和长期变化时间序列。这些地磁虚拟天文台（GVO）系列提供了一种方便的方法，可以全局监视和分析来自低地球轨道的地磁场的长期变化。该系列是通过将局部笛卡尔势场模型对Swarm的沿线轨迹和东西方求和值进行稳健拟合而获得的在每月1个月或4个月的时间窗内，在距GVO位置700公里半径内收集的卫星数据。我们描述了两种GVO数据产品：（1）“观测场” GVO时间序列，其中所有观测源都对估计值有所贡献，而没有任何数据选择或校正；以及（2）“核心场” GVO时间序列，其中有其他数据进行选择，然后应用降噪方案和逐周期球谐分析来减少磁层和电离层信号的污染。长期变化系列是核心领域GVO的年度差异。我们给出了结果群的例子GVO系列，通过与地面观测站和地磁场模型进行比较来评估其质量。在与六个高质量中低纬度地面观测站进行的基准比较中，我们发现，使用年度差异计算得出的核心场GVO场强度的长期变化，其均方根值分别为1.8 nT / yr和1.2 nT / yr。分别为1个月和4个月版本。GVO系列在空间和时间上定期采样，以及可获得的数据误差估计值，使其非常适合希望进行核心动力学数据同化研究或研究长期磁层和电离层信号及其感应对应物的用户。该群GVO的时间序列将大约每四个月定期更新一次，从而可以随时访问Swarm卫星的最新长期变化数据。