# Evaluation of GNSS-TEC Data-Driven IRI-2016 Model for Electron Density
## 4 Discussion and Conclusions  
The accuracy of the electron density of IRI-2016 and upda-IRI-2016 outputs driven by IG12 and IG-up was evaluated using ionosonde data and COSMIC data for 2015 and the first month of 2019, as well as all eligible COSMIC data for the whole year of 2015 (one day per week), respectively, in terms of the bottomside electron density and NmF2 are discussed and the following conclusions are drawn:  
1. It can be seen from both ionosonde data and COSMIC inversion electron density profiles that ionospheric electron densities, especially the peak electron density in the F2 layer, are larger in the years of high solar activity than in the years of low solar activity, which is in accordance with the law of the influence of solar activity on electron density. The trends in the variation of electron density with altitude of the IRI-2016 and upda-IRI-2016 outputs driven by IG12 and IG-up, respectively, are both consistent with the COSMIC electron density profiles from the COSMIC inversion. 2. The results of using ionosonde data as a reference and COSMIC data as a reference show that both the electron density and NmF2 output of upda-IRI-2016 driven by IG-up compared to IRI-2016 model driven by IG12 are greatly improved in both high and low solar activity years. 3. In terms of electron density, compared with IRI-2016 driven by IG12, the optimization effect of upda-IRI-2016 is more significant at low-latitude stations than at high-latitude stations. Compared to ionosonde, in January 2015, the PIs of MAE and RMSE are 32.5% and 32.6% for the Wuhan stations, respectively. The PIs are 31.2% and 31.4% for the Beijing stations, respectively. In January 2019, the PIs are 44.1% and 42.1% for the Wuhan stations and 16.5% and 16.0% for the Beijing stations, respectively. Compared to COSMIC, the PI for both MAE and RMSE exceeded 20.8% in 2015. 4. In terms of NmF2, the optimization effects of both low solar activity years and low-latitude stations are more significant than those of high solar activity years and high-latitude stations. Compared to ionosonde, in January 2015, the PIs of MAE \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Year**} & \multicolumn{2}{c}{**MAE (10\({}^{12}\) el/m\({}^{3}\))**} & \multirow{2}{*}{**PI**} & \multicolumn{2}{c}{**RMSE (10\({}^{12}\) el/m\({}^{3}\))**} & \multirow{2}{*}{**PI**} \\ \cline{2-2} \cline{5-6}  & **IRI-2016** & & & & **IRI-2016** & & **Upda-IRI-2016** \\ \hline
2015 & 0.1973 & 0.1462 & 25.9\% & 0.2936 & 0.2430 & 17.2\% \\ \hline \hline \end{tabular}
\end{table} 
Table 6: MAE, RMSE, and its precision improvement (PI) percentage for the difference between the NmF2 and COSMIC data for IRI-2016 and upda-IRI-2016 in 2015. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Year**} & \multicolumn{2}{c}{**MAE (10\({}^{12}\) el/m\({}^{3}\))**} & \multirow{2}{*}{**PI**} & \multicolumn{2}{c}{**RMSE (10\({}^{12}\) el/m\({}^{3}\))**} & \multirow{2}{*}{**PI**} \\ \cline{2-2} \cline{5-6}  & **IRI-2016** & & & **IRI-2016** & & **Upda-IRI-2016** \\ \hline
2015 & 0.1458 & 0.1223 & 15.6\% & 0.1649 & 0.1426 & 13.5\% \\
2019 & 0.0854 & 0.0599 & 29.9\% & 0.0932 & 0.0657 & 29.5\% \\ \hline \hline \end{tabular}
\end{table} 
Table 5: MAE, RMSE, and its precision improvement (PI) percentage for the difference between the NmF2 and COSMIC data for IRI-2016 and upda-IRI-2016 in January 2015 and January 2019.  
and RMSE are 45.3% and 41.2% for the Wuhan stations, respectively. The PIs are 15.8% and 11.8% for the Beijing stations, respectively. In January 2019, the PIs are 49.0% and 45.6% for the Wuhan stations and 29.0% and 22.0% for the Beijing stations, respectively. Compared to COSMIC, the PI was over 17.2% for the whole year of 2015 and over 29.5% for January 2019. The use of IG-up to drive the IRI-2016 model has not only led to a significant improvement in the accuracy of the TEC calculated by IRI-2016, but has also led to the optimization of the accuracy of its calculated electron density contours and peak electron densities.