Investigation of ionospheric TEC over China based on GNSS data

In this paper, the ionospheric total electron content (TEC) is derived from 250 Global Navigation Satellite Systems (GNSS) receivers over China. The GNSS TEC data are utilized to study the diurnal and day-to-day variability of ionosphere, ionospheric east–west differences and to construct regional ionospheric map. The GNSS–TEC curves clearly show sunrise and sunset enhancements in the diurnal variation. The peak value of TEC is lower in January 2015 than in May 2014. There is 2 h difference in the occurrence time of TEC maximum/minimum between May and January. Compared with the observations of Global Positioning System (GPS) and Global Navigation Satellite System (GLONASS), the measurements from the Geostationary Earth Orbit (GEO) satellites of BeiDou Navigation Satellite System (BDS) clearly present the ionospheric day-to-day variability and east–west differences in a region with small longitude differences (3.52–11.31°). The east–west differences in TEC are more obvious in larger longitude differences at 11:30 local time on 23 January 2015. The maximum east–west difference in TEC is about 7 total electron content unit (TECU, 1 TECU = 1016 el m−2) in longitude difference of 11.31°. Our analysis shows that the TEC for east–west small longitude differences may be associated with the east–west gradient of geomagnetic declination. Based on 250 GNSS stations, a regional TEC map constructed by Kriging method can well capture the main spatial structure of ionosphere in China. A comparison between TEC maps obtained by Kriging method and provided by Jet Propulsion Laboratory displays that there are large deviations in the North of China, which is mainly caused by the difference in the number of used GNSS stations. In addition, comprehensive investigation presents that GNSS has more advantages over GPS and GLONASS in the ionosphere research over China.