## 4 Technique Validation and Discussion
### Absolute Total Electron Content  
Figure 6 presents the results of the IRI-2012 simulating the TuRBOTEC algorithm operation (black dotted lines) for different stations: the mid-latitude IRKJ, equatorial NTUS, high-latitude THU2. The results were obtained for the 10 April 2012. One can see good qualitative and quantitative agreement of the vertical TEC recovery results with the IRI-2012 input data (red line). The average deviation for IRKJ by the absolute value is 0.1 TECU, maximal is 0.3 TECU, and RMS being 0.09 TECU. For NTUS, the average deviation is 0.4 TECU, maximal 0.95 TECU, RMS being 0.35 TECU. For THU2, the average deviation is 0.23 TECU, maximal \(-0.6\) TECU, RMS being 0.17 TECU. The differences between TuRBOTEC simulation and the IRI-plas vertical TEC are shown in green. The results show that TuRBOTEC provides even better performance for modeling based on IRI-plas at mid-latitudes, and comparable performance at low latitudes. Higher difference at high latitudes can be due to using \(\alpha\) obtained through the IRI-2012 modeling, so we used \(\alpha\)=0.96 for THU2. We did not find significant influence of the plasmosphere on TuRBOTEC estimations, except high latitudes, where we should to use another \(\alpha\) in (4). The greatest deviation occurs in the equatorial region. This is related to a substantially inhomogeneous ionosphere structure in this region, particularly, during daylight hours. The error is less at high latitudes. Figure 5: Contribution of measurements from individual satellites to the estimates at different instants. Although, as compared with the mid-latitude region, the error is higher. This is related to the absence of satellite observations at high elevations in high latitude regions, and to the dominance of the southward contribution to the total measurement statistics. Figure 7 presents the results of estimating the vertical TEC for IRKJ by real dual-frequency measurements from GPS and GLONASS (red line). The dot-and-dash blue line and the dotted black line show the data on GIMs from the JPL and CODE laboratories, respectively. The data are presented for the 5 March 2015 quiet conditions (left panel, \(Kp_{max}=2.3\), maximal \(Kp\) for the day) and for the 17 March 2015 magnetic storm (right panel, \(Kp_{max}=7.7\)). One can see well that the TEC curves reproduce the diurnal variation similarly, but they can quantitatively differ. Such systematic differences are well-known and were repeatedly addressed in literature [57]. Like discussed earlier, the JPL data, as a rule, surpass the data from other laboratories. One can see that, at individual instants, synchronous variations with TEC are noted in the CODE and TuRBOTEC data. For example, for the 17 March 2015 strong magnetic storm, one can see a slight increase in the vertical TEC around 18 UT. In general, the estimates for the vertical TEC appear plausible for all the considered cases. Deviations in the data from other laboratories are within the variance interval of different laboratories among themselves. To analyze systematic variances, we built a histogram for the \(\Delta I_{V}\) difference distribution between the vertical TEC data in the Irkutsk region. Figure 6: Results of simulating the absolute vertical TEC recovery for different stations as 10 April 2012: (**a**) mid-latitude IRKJ, \(\alpha=0.97\); (**b**) equatorial NTUS, \(\alpha=0.87\); (**c**) high-latitude THU2, \(\alpha=0.94\). The black dotted line shows the results of the TuRBOTEC operation, the red line exhibits the IRI-2012 vertical TEC data, and the blue line shows differences between the results of the TuRBOTEC operation and the IRI-2012 model. The green line shows the similar differences, but for the IRI-plas simulation. The axis for the blue and green lines are on the right, for the red and black lines on the left. Figure 7: Absolute vertical TEC recovered from real the GPS/GLONASS data for IRKJ (red line). Panel (**a**) is for 5 March 2015 (\(\text{Kp}_{\text{max}}=2.3\)), panel (**b**) 17 March 2015 (\(\text{Kp}_{\text{max}}=7.7\)).