Ingestion of GIM-derived TEC data for updating IRI-2016 driven by effective IG indices over the European region
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In order to adapt the International Reference Ionosphere (IRI) model from ionospheric climatological model to near real-time weather predictions, total electron content (TEC) data from Global Ionosphere Maps are ingested into the IRI-2016 model through retrieving the optimal ionospheric index (IG) over Europe on an hourly basis. When the retrieved hourly effective IG indices are used to drive the IRI-2016 model, the resulting ionospheric parameters are externally evaluated with respect to multiple sources, including the COSMIC/ionosonde electron density (Ne) profiles, ionosonde F2 layer critical frequency (foF2), and individual GNSS-derived TEC for both quiet and storm conditions. Results show that: (1) The updated IG indices for different latitudinal zones tend to follow a similar trend under quiet conditions, but vary much more significantly during storm days. (2) The retrieved Ne profiles from the updated IRI-2016 agree better with those from the COSMIC Ne profiles, especially for the F2 layer maximum electron density (NmF2) values. Furthermore, the updated IRI-2016 Ne profiles show improved agreement with ionosonde measurements under quiet conditions, particularly for the bottom-side Ne profiles and NmF2 as well as for the storm-time Ne profiles. (3) Comparing the IRI-updated TEC with the GNSS-derived TEC, IRI-updated TEC improved approximately 19% for both quiet and storm days, and the nighttime TEC improvement is better than that during daytime. When compared to the ionosonde foF2 measurements, the daytime IRI-updated foF2 improvement during quiet time is better than that during storm condition, while the performance for nighttime foF2 drops during quiet time. Discussions about possible reasons for the nighttime foF2 degradation are included.
KeywordsGIM-derived TEC IRI-2016 IG index Ingestion method
This work was supported by the National Key Research and Development Program of China (No. 2016YFB0501803), the National Natural Science Foundation innovation research group project (No. 41721003). S. Zou acknowledges NSF AGS 1400998. The GNSS data are archived from the EUREF Permanent Network (http://epncb.oma.be/), the ionosonde data were downloaded from the NOAA website (ftp.ngdc.noaa.gov/ionosonde/data/), and the IONEX files that contain the GIM-derived TEC are available at ftp://cddis.nasa.gov/pub/gps/products/ionex/. The COSMIC radio occultation data are available at CDDAC (http://cdaac-www.cosmic.ucar.edu/cdaac/). The geomagnetic/solar activity indices data are obtained from the NASA Goddard Space Flight Center (https://spdf.gsfc.nasa.gov/index.html).
All authors made great contributions to the work. Yibin Yao and Shasha Zou designed the research; Lei Liu and Jian Kong performed the research; Lulu Shan, Changzhi Zhai, Cunjie Zhao and Youkun Wang analyzed the data; and Lei Liu and Shasha Zou wrote the paper.
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