Climatological Statistics of Extreme Geomagnetic Fluctuations With Periods From 1 s to 60 min

Using a global database of 125 magnetometers covering several decades, we present occurrence statistics for fluctuations the horizontal geomagnetic field (dBh/dt) exceeding 99.97th percentile (P99.97) both ramp changes (Rn) and root-mean-square (Sn) over periods, ?, from 1 to 60 min describe their variation with latitude magnetic local time (MLT). Rates exceedance are explained by reference magneto-ionospheric processes dominant in different MLT sectors, including ULF waves, interplanetary shocks, auroral substorm currents, traveling convection vortices. By fitting generalized Pareto tail distributions above P99.97, predict return levels (RLs) Rn Sn periods between 5 500 years. P99.97 RLs increase monotonically frequency (1/?) (with few exceptions at latitudes) this is well modeled quadratic functions whose coefficients vary smoothly latitude. For UK providing 1-s cadence measurements, analysis extended cover s empirical Magnetotelluric Transfer used percentiles geoelectric wide range (2 × 10?4 4 10?2 Hz) assuming sinusoidal fluctuation. These results help identify principal causes leading extreme geomagnetically induced currents (GIC) ground infrastructure timescales they inform choice dependence use dBh/dt as GIC proxy.