Research on Geomagnetic Secular Variation of China and Surrounding Areas Based on The Geomagnetic Virtual Observatories

The Low Earth Orbit (LEO) geomagnetic satellites provide a large number of high-precision measurements, which are crucial for researching the Secular Variation (SV) of the geomagnetic field. We employ the combined constellation data from the Chinese Seismo-Electromagnet Satellite (CSES) and Swarm satellites to extract the SV in China and surrounding areas, based on the Geomagnetic Virtual Observatory (GVO) method. On this basis, we have developed two GVO products: the core field, and the SV series. The accuracies of these products are assessed using ground observatories measurements and geomagnetic field model. Moreover, the results indicate that the GVO products align well with the series from ground observatories and the CHAOS model. The majority of root-mean-square deviation (RMSE) values of the core field series are less than 5 nT, consistent with the INTERMAGNET standards for quasi-definitive data. In the GVO core field series, the maximum accuracy of one-month and four-month intervals are 2.24 nT and 1.16 nT, respectively. In the GVO SV series, the maximum accuracy of one-month and four-month intervals are 2.03 nT/yr and 1.36 nT/yr, respectively. The GVO SV series effectively capture geomagnetic jerks from ground observatories without losing temporal resolution. We demonstrate that the GVO method serves as an effective and precise tool for extracting SV information of the geomagnetic field. In the GVO products, the RMSE of the horizontal component exceeds that of the vertical component, and the magnitude of RMSE deviation correlates with solar activity levels. With more and more geomagnetic satellites in orbit, we wish to use multi-constellation magnetic satellite data to assess the geomagnetic field more accurately.