Extreme value theory applied to the auroral electrojet indices

The study of extreme weather and space events has gained paramount importance in modern society owing to rapid advances in high technology. Understanding and describing exceptional occurrences plays a crucial role in making decisive assessments of their potential impact on technical, economic, and social aspects in various fields. This research focuses on analyzing the hourly values of the auroral electrojet (AE) geomagnetic index from 1957 to 2019 by using the peak over threshold method in extreme value theory. By fitting the generalized Pareto distribution to extreme AE values, shape parameter indices were derived, revealing negative values that establish an upper bound for this time series. Consequently, it became evident that the AE values had reached a plateau, suggesting that extreme events exceeding the established upper limit are rare. As a result, although the need for diligent precautions to mitigate the consequences of such extreme events persists, surpassing the upper limit of AE values becomes increasingly challenging. It is also possible to observe an aurora in the middle- and low-latitude regions during the maximum period of the AE index.