Geomagnetic Virtual Observatories: monitoring geomagnetic secular variation with the Swarm satellites
Geomagnetic Virtual Observatories: monitoring geomagnetic secular variation with the Swarm satellites
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DOI：
10.1186/s40623-021-01357-9
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发表时间：
2021-02-19
影响因子：
3
通讯作者：
Finlay, Christopher C.
中科院分区：
文献类型：
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作者：
Hammer, Magnus D.;Cox, Grace A.;Finlay, Christopher C.
我们提出了地磁主磁场和长期变化的时间序列，在300个等面积分布的位置，在490公里的高度，来自三个群卫星收集的磁场测量。这些地磁虚拟天文台系列为从低地球轨道全球监测和分析地磁场的长期变化提供了一种方便的手段。该系列是通过本地笛卡尔势场模型的鲁棒拟合获得的沿轨道和东西总和和差异的群卫星数据收集的GVO位置在半径为700公里的范围内，在1个月或4个月的时间窗口。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贡献，没有任何数据选择或校正，（2）“核心场”GVO时间序列，其中进行额外的数据选择，然后应用去噪方案和逐历元球谐分析来减少磁层和电离层信号的污染。长期变化系列作为核心场GVO的年度差异提供。我们提出的例子所产生的群GVO系列，通过与地面观测站和地磁场模型的比较，评估其质量。在与6个高质量的中低纬度地面观测站的基准比较中，我们发现核心场GVO场强的长期变化，使用年度差异计算，同意1个月和4个月的版本，分别为1.8 nT/yr和1.2 nT/yr的均方根。由于在空间和时间上定期取样，并提供数据误差估计，全球静止轨道观测器系列非常适合希望对核心动力学进行数据同化研究或研究长周期磁层和电离层信号及其感应信号的用户。Swarm GVO时间序列将定期更新，大约每四个月更新一次，以便随时获得Swarm卫星的最新长期变化数据。
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.