A Limit for the Values of the Dst Geomagnetic Index

The study of the extreme weather space events is important for a technological-dependent society. Extreme value theory could be decisive to characterize those extreme events in order to have the knowledge to make decisions in technological, economic, and social matters, in all fields with possible impacts. In this work, the hourly values of the Dst geomagnetic index have been studied for the period 1957-2014 using the peaks-over-threshold technique. The shape parameter obtained from the fit of the generalized Pareto distribution to the extreme values of the |Dst| index leads to a negative value implying an upper bound for this time series. This result is relevant because the estimation of this limit for the extreme values leads to 850 nT as the highest expected value for this geomagnetic index. Thus, from the previous characterization of the Carrington geomagnetic storm and our results, it could be considered the worst-case scenario. Plain Language Summary The study of the space environment that surrounds the Earth is relevant due to the negative effects that unfavorable conditions cause to technological systems. The geomagnetic Dst index is used in this work in order to evaluate the severity of the magnetic storms. The use of statistical tools specifically designed to study rare and scarce extreme events is applied to understand the behavior of this geomagnetic index. The results show that there is a limit value for the geomagnetic Dst index, and therefore, previous registered extreme storms could be considered as the "worst case scenario".