Investigation of Solar Flares Impact on GPS/BDS/GALILEO Broadcast Ionospheric Models

The ionosphere is significant to solar-terrestrial space environment, and the ionospheric delay is considered as one main error source in Global Navigation Satellite System (GNSS). For GNSS single-frequency users, broadcast ionospheric models (BIMs) play an important role in mitigating the ionospheric delay. Solar activity induces ionospheric disturbances, which can reduce the performance of GNSS. In this study, solar flares impact on Global Positioning System/BeiDou satellite navigation System/Galileo (GPS/BDS/GALILEO) BIMs was investigated in the Asia-Pacific region. Twelve X-class and M-class large solar flares were selected for this study. Total electron content (TEC) derived from selected International GNSS Service and Crustal Movement Observation Network of China (CMONOC) were used to analyze the TEC anomalies and the adaptability of the GPS/BDS/GALILEO BIMs during sample solar flare events. It is verified that very noticeable sudden increase in TEC clearly took place during solar flares. The temporal variation of rate of TEC is more pronounced and rapid with respect to that of TEC. Especially, solar flares impact on the correction accuracy of the GPS/BDS/GALILEO BIMs is significant, as illustrated by a noticeable decrease in relative difference between the observed and modeled TEC values of the GPS/BDS/GALILEO BIMs occurred during the events. Through our investigation, we found that the adaptability of BDS BIM is better than GPS and GALILEO BIMs under solar flare conditions because its coefficients were updated more frequently, while the accuracy of the GALILEO BIM is the highest among current GPS/BDS/GALILEO BIMs in general.