## 3 Results
### Analysis of Ionospheric DVTEC Disturbances
#### 3.2.1 DVTEC Variations Due to Thunderstorms  
Three geographical zones were defined for analysis purposes, as illustrated in Figure 9. In addition, the figure shows the RAMSAC stations and the lightning counts on a grid of a 0.2\({}^{\circ}\) by 0.2\({}^{\circ}\) cells. The working zones represent the following:  
* Zone 1: The thunderstorms' region;
* Zone 2: The region around the thunderstorms and adjacent to them; and
* Zone 3: The area away from the thunderstorms. Figure 10 illustrates the variation in DVTEC on 10 November 2018 across multiple stations and GNSS satellites. This figure provides a visual representation of the DVTEC changes observed within the specified analysis zones. Results from each station are vertically offset from the previous station by 1 TECU (\(10^{16}\) electrons/m\({}^{2}\)). In each plot, the three time intervals defined in the previous section are marked with different colors in the horizontal axis in decimal time. The interval from 0 UTC to 2.66 UTC (i.e., 00:00 UTC-02:40 UTC) is marked in blue, the interval from 2.66 UTC to 5.33 UTC (i.e., 02:40 UTC-05:20 UTC) is marked in yellow, and the interval from 5.33 UTC to 8 UTC (i.e., 05:20 UTC-08:00 UTC) is marked in green. Additionally, on each graph, the names of the stations exhibiting large deviations in DVTEC, with peak-to-peak amplitudes greater than 1 TECU, are highlighted in light blue on the vertical axis. Comparing the graphs in Figure 10, it is observed that the signals became progressively more unstable, especially in Zone 3 (see in Figure 10c). Analyzing the temporal evolution of the signals within each zone, it is evident that the most significant magnitude variations occurred during the interval from 02:40 UTC to 05:20 UTC, coinciding with the peak in thunderstorm electrical activity. The analysis performed showed that the peak-to-peak amplitudes of the DVTEC variations were different for each station and satellite. Figures 11-13 present the positions of the RAMSAC stations and their respective peak-to-peak DVTEC amplitude ranges. The peak-to-peak amplitude ranges were calculated for each time interval, i.e., the peak-to-peak amplitude range corresponding to the period 00:00 UTC-02:40 UTC is presented in the upper left panel, the amplitude range for the interval 02:40 UTC-05:20 UTC in the upper right panel, and the range for 05:20 UTC-08:00 UTC in the lower left panel. The figures also include the lightning counts plotted on the 0.2\({}^{\circ}\) by 0.2\({}^{\circ}\) grid for each of the analyzed time periods. Each station is represented by a diamond, whose color indicates the peak-to-peak DVTEC range measured at that station. The locations of the events reported by the Earth Networks system to have the maximum peak currents for the different discharge types are represented by stars. Figure 10: Temporal variations in the differential vertical total electron content (DVTEC) of the RAMSAC stations within (**a**) Zone 1, (**b**) Zone 2, and (**c**) Zone 3. On the x-axis, with colored bars, the three time periods analyzed in the previous section are represented, blue for the period 00:00 UTC-02:40 UTC (i.e., 21:00 LT-23:40 LT), yellow for the interval 02:40 UTC-05:20 UTC (i.e., 23:40 LT-02:20 LT), and green for the period 05:20 UTC-08:00 UTC (i.e., 02:20 LT-05:00 LT). On the y-axis, the stations are located 1 TECU apart. A scale is shown in the figure as a reference. The stations with the largest deviations observed in DVTEC are outlined in blue. Figure 9: Lightning counts on the 0.2\({}^{\circ}\) by 0.2\({}^{\circ}\) grid from 00:00 UTC to 08:00 UTC (21:00 LT-05:00 LT). Light colors represent locations with the highest lightning counts. RAMSAC stations are marked with diamonds, and the three study zones are delimited with ellipses. In the period 00:00 UTC-02:40 UTC (i.e., 21:00 LT-23:40 LT), a predominance of peak-to-peak DVTEC amplitudes between 0.21 TECU and 0.44 TECU was observed in all three zones. In Zones 1 and 2, peak-to-peak DVTEC amplitudes averaged 0.3 TECU, while, in Zone 3, they averaged 0.22 TECU.