Extreme Value Analysis of Ground Magnetometer Observations at Valentia Observatory, Ireland

Understanding global space weather effects is of great importance to the international scientific community, but more localized space weather predictions are important on a national level. In this study, data from a ground magnetometer at Valentia Observatory is used to characterize space weather effects on the island of Ireland. The horizontal component of magnetometer observations and its time derivative are considered, and extreme values of these are identified. These extremes are fit to a generalized extreme value distribution, and from this model return values (the expected magnitude of an observation within a given time window) are predicted. The causes of extreme values are investigated both in a case study, and also statistically by looking at contributions from geomagnetic storms, substorms, and sudden commencements. This work characterizes the extreme part of the distribution of space weather effects on Ireland (and at similar latitudes), and hence examines those space weather observations which are likely to have the greatest impact on susceptible technologies. Plain Language Summary Space weather describes the effects of the interaction between the Sun's solar wind and the Earth's magnetic field, and can have dramatic impacts on human technology. Space weather can be characterized both globally, and on a local level. In this study, space weather over the island of Ireland is characterized using an Irish ground based magnetometer at Valentia Observatory. Magnetometers record a measure of the magnetic field, and these changes will be large when space weather effects are enhanced. Extreme observations from this magnetometer are detected, and these are used to predict future extreme observations. Additionally, the contributions of different types of space weather phenomena to extreme observations are determined. Understanding extreme observations on a national level will help to enhance space weather resilience which is increasingly important as society becomes more and more dependent on technology. Key Points More extreme Valentia observations are observed in the premidnight sector Return values of extreme Valentia observations at given return periods are predicted Geomagnetic storms contribute more extremes than substorms or sudden commencements