Improved IRI-2016 model based on BeiDou GEO TEC ingestion across China

Due to the quasi-invariant orbital locations of the BeiDou geostationary earth orbit ( GEO) satellites, the BeiDou GEO total electron content (TEC) is not influenced by the contamination of ionospheric spatial and temporal gradient variations. We ingest BeiDou GEO TEC observations across China into the IRI-2016 model for the first time by developing effective hourly ionospheric global indices (IG), which were estimated based on the assumption that BeiDou GEO TEC is equal to the updated IRI TEC for the given location and time. When the retrieved hourly IG indices are used to drive the IRI-2016 model, the resulting near real-time ionospheric parameters are externally evaluated by other data sources, including (1) the Center for Orbit Determination of Europe (CODE) Global Ionosphere Maps (GIM) TEC products and extra BeiDou GEO TEC, (2) Constellation Observing System for Meteorology, Ionosphere and Climate (COSMIC) electron density (Ne) profiles and F2 layer maximum electron density (NmF2) and (3) ionosonde Ne profiles and critical frequency (foF2) observations under both geomagnetic quiet and active conditions. The validation results show that the proposed ingestion technique successfully pushes the standard IRI model toward being usable for near real-time weather predictions. Moreover, a general improvement in accuracy of the updated IRI model regarding TEC, Ne, NmF2 and foF2 can be obtained during September 2-12, 2017, as expected: (1) updated TEC BIAS/RMS reduces from - 3.20/4.86 to - 0.10/1.86 TECU compared to CODE GIM, and from - 2.84/4.63 TECU to 0.75/1.05 TECU compared to external BeiDou GEO TEC. (2) Topside electron density from updated IRI matches better with that from the COSMIC than the standard IRI; the STD/RMS/BIAS versus COSMIC NmF2 decreases from 2.195/2.313/0.845 to 2.083/2.043/- 0.092 (unit: -10(5) cm(-3)). (3) Bottomside electron density from the updated IRI is much closer to the ionosonde measurement than the standard IRI; updated IRI foF2 also exhibits relatively minor improvements compared with ionosonde measurements, i.e., STD/RMS/BIAS reduces from 1.070/1.268/0.681 to 1.019/1.061/-0.298 MHz.