## Appendix B  
This is the additional explanatory text for the exact calculation steps, how the geographic and geomagnetic latitudes corresponding to the green and red auroras during the main phase of the superstorm were calculated. Most studies regarding the aurora concentrate on the determination of the peak emission height of the aurora borealis and not the height boundaries of each type (color) of aurora. Since the accurate height of a given type (color) of aurora for this superstorm is currently not known and since the behavior of the aurora can differ storm by storm (andthere can be differences at mid-latitude compared to high-latitude cases), here the upper boundary of the auroras is based on statistical observations (with this, the height is supposed to be overestimated). Regarding the green aurora, after the study of [PERSON] et al. [51] the correlation coefficient of the peak emission height of the green aurora is around 0 at 180 km height (see Figure 1 in the article of [51]), that is why 180 km was chosen as an overestimation for the upper height boundary of the green aurora. For the height determination of the red aurora, we used the study of [PERSON] et al. [52]. The correlation coefficient of the peak emission height was close to 0 at 300 km (see Figure 2 in the article of [52]), therefore, the 300 km height was chosen as upper boundary height for the red aurora position calculations in our study. To estimate the geographical location of the auroral borealis, the images of all-sky cameras were used (e.g., Figure 10). Based on the configuration of the all-sky images (Figure 21a) the distances (b, c) and the viewing angles (\(\beta,\gamma\)) are directly proportional and can be determined. Therefore, the equation is  
\[\frac{\mathrm{b}}{\mathrm{r}}\cong\frac{\beta}{90^{\circ}},\frac{\mathrm{c}}{ \mathrm{r}}\cong\frac{\gamma}{90^{\circ}} \tag{1}\]  
In the next step x (the average of three different measurements taken from the picture) was used instead of r, since the radius of the all-sky image is unknown, because the pictures are from outside source, see Acknowledgement. On Figure 22a the x and y (the proportion of the aurora on the captured image) can be measured and quantified from the images. From x and y, the angle \(\alpha\) (angle between the location of the all-sky camera and the top of the aurora, Figure 22b) can be calculated:  
\[\frac{\mathrm{y}}{\mathrm{x}}=\frac{\alpha}{90^{\circ}} \tag{2}\]  
The h is the maximum height of the different type (color) of observed aurora, and were chosen as described above (180 km for the green aurora and 300 km for the red aurora), therefore the horizontal distance between the camera and the exact location of the aurora (d) can be estimated with this equation:  
\[\frac{\mathrm{h}}{\mathrm{d}}=\tan(\mathrm{a}) \tag{3}\]  
The exact calculation for 20:30 UT is as follows:  
The subauroral arc (SAR) was at zenith at this time, and directly above Szombathely, Hungary (47.25\({}^{\circ}\)N lat, 42.25\({}^{\circ}\)N mlat, see Figure 23 for the location). For the red aurora with Equation (2), where y = 4.8, x = 9.3 and after the calculation  
\[\frac{4.8}{9.3}.90^{\circ}=46.45^{\circ},\]  
the top of the red aurora was visible around 46.45\({}^{\circ}\) degrees. Using the above-mentioned h = 300 km upper height for the red aurora (after [52]), the d value is determined with Equation (3) as follows:  
\[\frac{300}{\tan 46.45^{\circ}}=285.7\]  
As a result, the estimated horizontal distance between the camera (Szombathely) and the red aurora is around 285.7 km, so the aurora was above Prague (50.06\({}^{\circ}\)N lat, 49.45\({}^{\circ}\)N mlat, see Figure 23). The ionograms from Pruhonice station (next to Prague, Figure 23) seems to confirm this, see Figure 24 (source: [[https://giro.uml.edu/ionoweb/#](https://giro.uml.edu/ionoweb/#)]([https://giro.uml.edu/ionoweb/#](https://giro.uml.edu/ionoweb/#)) (accessed on 8 July 2025).