Temporal, directional, and spatial statistics of extreme dB/dt

Neil Rogers - Lancaster University; James Wild - Lancaster University, United Kingdom; Emma Eastoe - Lancaster University, United Kingdom

Session: Ground-Level Geomagnetically Induced Currents

Abstract

Extreme geomagnetic fluctuations (dB/dt) have previously been modelled from 1-min cadence data.  In this talk we show how occurrence rates for large and extreme dB/dt vary are modelled on timescales from 1 s to 60 min for both ramp changes (i.e. the change in B over n minutes) and RMS variations (of 1-min dB over n minutes), and examine their dependence on geomagnetic latitude, local time, and compass direction.  For the 1-min dataset, we also summarise (i) new methods to improve return level estimates by combining generalised Pareto distributions from multiple directional sectors, and (ii) an assessment of the spatial coherence of extremes in dB/dt (pairwise extremal dependence between magnetometer sites worldwide).