# Effects of the 12 May 2021 Geomagnetic Storm on Georeferencing Precision
## 4 Discussion and Main Conclusions
### Positioning Errors
The ROTI also has an intriguing behavior. We observe an increase in the number of stations with ROTI > 0.25 TECu/min (Figure 5) especially in the poles and the South American region. In North America and northern Europe region, the number of stations with activity increased from 50% to 94%. In the Antarctic region, there was an increase from 12% to 62% of stations with activity. In South America, the percentage passed from 1.5% to 10.5% of the stations with activity. Nevertheless, we do not find a significant increase in the number of stations with higher positioning errors over the poles. Therefore, it is conclusive that the fast variations of TEC might be responsible for the variations over the South American sector. Our results did not confirm that positioning errors increased rapidly with increasing ROTI (Figures 2d-f, j, 4g,h, 5 and 7; Table 4) as several studies suggest [56; 57; 58; 60]. Therefore, our results suggested that position errors also occur, regardless of whether the ROTI has rapid variations, if it is ROTI < 0.25 TECu/min or no ROTI variations are appreciated. In summary, the analyzed data show that the moderate 12 May 2021 geomagnetic storm strongly affected the GNSS precision for about an hour in several GNSS receivers, mainly on stations located in the South American sector. Comparison with previous moderate storms (27 March 2017 and 5 August 2019) showed that the effects in the position estimation are not directly deducible from the geomagnetic storms characteristics. The three analyzed storms were moderated, although the 12 May 2021 storm had a higher Kp, which tends to be a good indicator of midlatitude activity. By using three stations we compare the effects of the three storms, showing that the effects are stronger on the South American sector even though the ionospheric effects (DVTEC) are not severe. The positioning error data show that the horizontal coordinates are more robust to TEC perturbations, although the error in the vertical component is still high. In the literature, the vertical coordinate tends to be neglected, but for current and future GNSS applications, it might be relevant. It could be important for autonomous aerial applications or for high-precision activities. The mining, agriculture, fishing, and disaster-control sectors in Chile are starting to adopt autonomous or tele-operated systems that might be sensitive to ionopsheric perturbations. The relevant height of the vehicles in these industries might impose a serious risk for infrastructure or people if the vertical error in the GNSS receiver skyrockets. For instance, for open-pit mines, a high vertical error may cause a failure in the estimation of the terrace in which a vehicle is with the consequent risk of falling. Potential risks could be reduced by stopping autonomous operations during these events. However, our results show that it is hard to predict when a storm will have serious effects over the position accuracy. False positives in the forecasting can be complex for these industries, since stopping operation even for a short time, such as an hour, could be prohibitively expensive. The new solar cycle is critical to unravel the relation between solar activity and positioning errors in the GNSS receivers thanks to the large number of GNSS stations available around the world, gathering relevant data. However, we need to process the data in a standardized manner that facilitates comparison between different cycles, paying attention to the storms that produce unexpected behaviors such as those in the 12 May 2021 geomagnetic storm. Conceptualization, J.C.V.-A. and M.A.D. ; data curation, J.C.V.-A., M.A.D., J.C.B., and Y.S.-S.; formal analysis, J.C.V.-A. and M.A.D. ; funding acquisition, M.A.D. ; investigation, J.C.V.-A., M.A.D., J.C.B., and Y.S.-S.; methodology, J.C.V.-A. ; project administration, M.A.D. ; resources, M.A.D. and J.C.B. ; software, J.C.V.-A. and Y.S.-S.; supervision, M.A.D. ; validation, J.C.V.-A., M.A.D., J.C.B., and Y.S.-S.; visualization, J.C.V.-A. and Y.S.-S.; writing--original draft, M.A.D.