# Towards a Real-Time Description of the Ionosphere:
## 6 Validation Results for _fo_F2 Based on Radio Occultation Observations  
The full COSMIC dataset, comprising 1,791,602 selected electron density profiles measured from 2006 to 2018, was used to retrieve reliable _fo_F2 values for calculating the two-dimensional density plots of IRI-_fo_F2 vs. COSMIC-_fo_F2 and IRTAM-_fo_F2 vs. COSMIC-_fo_F2, along with the histograms of corresponding residuals, as shown in Figure 19. Differently from Figure 3, Figure 19 shows that IRTAM does not improve the _fo_F2 modeling accuracy of IRI. In fact, the IRTAM statistical distribution of residuals around the zero value, very similar to the IRI one, shows a value of _Res. Mean_\({}_{\rm IRTAM}\) = 0.095 MHz that is a little bit greater than _Res. Mean_\({}_{\rm IRI}\) = 0.067 MHz. Moreover, the comparisons \(RMSE_{\text{IRTAM}}\) = 1.120 MHz vs. \(RMSE_{\text{IRI}}\) = 1.053 MHz and \(NRMSE_{\text{IRTAM}}\) = 17.748% vs. \(NRMSE_{\text{IRI}}\) = 16.668% show a slight worsening of the _fo_F2 modeling precision made by IRTAM. This is also supported by the IRTAM density plot which appears more scattered than the IRI one (\(R_{\text{IRTAM}}\) = 0.888 vs. \(R_{\text{IRI}}\) = 0.901). However, given that the statistical quantities calculated with the two models do not differ significantly, we can claim that the IRI and IRTAM performances based on the COSMIC _fo_F2 data can be considered somewhat comparable. The statistical results reported in the following Table 4 show that only in a few cases is _Res. Mean_\({}_{\text{IRTAM}}\) < _Res. Mean_\({}_{\text{IRI}}\), while in all cases \(RMSE_{\text{IRI}}\) < \(RMSE_{\text{IRTAM}}\), \(NRMSE_{\text{IRI}}\) < \(NRMSE_{\text{IRTAM}}\), and \(R_{\text{IRI}}\) > \(R_{\text{IRTAM}}\). This means that the same concerns held for the entire COSMIC _fo_F2 dataset (Figure 19) hold also when IRI and IRTAM performances are evaluated on the COSMIC _fo_F2 time series binned according to the procedures described in Section 4.2, and considering the three levels of solar activity defined in Section 3.1. Figure 19: Density plots between measured (\(x\)-axis) and modeled (\(y\)-axis) _fo_F2 values, for (**a**) IRI and (**c**) IRTAM. Measured values are those from the entire COSMIC dataset. The black solid lines represent the best linear fit. Corresponding slope and intercept values, along with the correlation coefficient, are reported in the upper left box of each plot. Statistical distributions of the residuals between _fo_F2 values measured by COSMIC and corresponding values modeled by (**b**) IRI and (**d**) IRTAM. Corresponding _Res. Mean_, _RMSE_, and _NRMSE_ values, along with the total number of counts on which the statistics is based, are reported in the upper left box of each plot. In order to provide a comprehensive picture of how IRI and IRTAM models behave when the COSMIC _foF_2 dataset is considered for validation, global maps of IRI and IRTAM _RMSPE_ values were calculated along with the corresponding maps of the differences (\(RMSE_{\text{IRTAM}}-RMSE_{\text{IRI}}\)). It is important to note that for validating both models in terms of spatial, diurnal, seasonal, and solar activity variability, the maps were calculated binning IRI, IRTAM and (IRTAM-IRI) _RMSPE_ values as a function of: geographic latitude vs. geographic longitude, modip vs. LT hour, modip vs. doy, and modip vs. F10.7\({}_{81}\) (see Figures 20-23).