An Ionospheric Space Weather Data Assimilation System over China based on Meridian Project GNSS Measurements

The successful deployment and national acceptance of the second phase of the Chinese Meridian Project (CMP), a major national scientific and technological infrastructure, signify a substantial leap forward in China’s space environment monitoring capabilities. In particular, CMP’s ionospheric monitoring network has greatly strengthened both research and operational capabilities in ionospheric space weather. This study presents a new-generation ionospheric space weather data assimilation system for China and adjacent regions, based on GNSS observations from the CMP. Leveraging stable and robust data from 85 GNSS stations from CMP and the International GNSS Service, the system integrates multi-constellation GNSS measurements from GPS, GLONASS, Beidou, and Galileo as input and employs a three-dimensional variational assimilation approach. It generates high-precision and operational ionospheric space weather products, represented by ionospheric TEC, covering China and adjacent regions (15^o-55^oN，70^o-140^oE), which significantly improves the ability to reconstruct and characterize ionospheric disturbances over China. This data assimilation system can provide diverse ionospheric space weather products, including gridded TEC, delta TEC, and the Rate of TEC Change Index (ROTI), with a high spatial-temporal resolution of 1°×1° and 15 minutes. These ionospheric products are routinely updated and publicly available via the website of Space Environment Prediction Center (http://www.sepc.ac.cn/TEC_chn.php) at the National Space Science Center, Chinese Academy of Sciences. Beyond enabling high-fidelity monitoring of the ionospheric space environment over China and adjacent regions, this system also supports in-depth investigation of multi-scale ionospheric variations and irregularity characteristics. In addition, it delivers timely, accurate, and effective ionospheric error correction and space weather information for satellite navigation, radar imaging, shortwave communication, and space weather nowcasting.