Monitoring and prediction of ionospheric spatial gradients from global ionosphere maps: a comparative analysis

Abstract

The spatial gradient of the ionospheric electron content critically influences the accuracy and reliability of Global Navigation Satellite System (GNSS) real-time positioning services. The real-time monitoring and prediction of ionospheric spatial gradients are prerequisites for enhancing global positioning performance. We propose to utilize real-time and predicted Global Ionosphere Maps (GIMs) for the monitoring of ionospheric spatial gradients on a global scale. A comprehensive evaluation of ionospheric spatial gradient monitoring capability based on real-time and predicted GIMs is performed across varying solar activity periods and geomagnetic conditions from 2021 to 2024. The long-term spatial gradient variation of real-time and predicted GIMs (UADG and UN0G) exhibits a noticeable increase in gradient error as solar activity intensifies. In 2024 (high solar activity), the spatial gradient error of real-time and predicted GIMs increased by 2 to 3 times compared to 2021 (low solar activity). The Pearson correlation coefficient exceeding 0.7 between the solar activity index F10.7​ and the standard deviation of spatial gradient errors of real-time GIMs as well as predicted GIMs underscores a strong relationship. Analysis of the three-year experiment indicates that the longitudinal gradient errors of the high latitude region are more profound than in mid- and low-latitude regions, whereas the latitudinal gradient errors in low latitude region is significantly higher than in mid- and high-latitude regions. Despite peak solar activity in 2024, the overall standard deviation of gradient error of real-time and predicted GIMs remains below 10 mTECU/km (corresponds to regular diurnal variation below 1–2 mm/km, in GPS L1 delay units). Time-series and year-by-year statistics of real-time and predicted GIMs during all geomagnetic storms from 2021 to 2024 demonstrate that the performance gap between real-time and predicted GIMs widens significantly during periods of high solar activity and increased geomagnetic disturbance. During strong geomagnetic storms (Kp ≥ 7), the error of the predicted UN0G can be 140% higher than the real-time WRTG. Furthermore, zonal negative-gradient errors of predicted GIMs show a particularly sharp increase, with the annual mean error of UN0G worsening from − 6.4 to − 41.1 mTECU/km, underscoring severe performance degradation under extreme space weather conditions. Results demonstrate that real-time GIMs are able to effectively monitor global ionospheric spatial gradients under both quiet and geomagnetic storm conditions. In contrast, there is room for improvement in the predicted GIMs to accurately forecast spatial gradients during disturbed conditions.

This research has been partially performed in the context of the National Natural Science Foundation of China (Grant No. 42404039 and No. 42174037), China Postdoctoral Science Foundation (Grant No. 2024T170220 and No. 2023M730943) , Young Talent Support Plan of Henan Association for Science and Technology (Grant No. 2024HYTPO27), Natural Science Foundation of Henan Province (Grant No. 242300421643), European Union PITHIA-NRF (Grant H2020-INFRAIA-2018-2020101007599) and DISPEC (Grant HORIZON-CL4-2023-SPACE-01-71) projects.

Peer Reviewed

Postprint (author's final draft)