Climatological Statistics of Extreme Geomagnetic Fluctuations with Periods from 1 s to 60 min

Rogers, Neil and Wild, James and Eastoe, Emma and Huebert, Juliane (2021) Climatological Statistics of Extreme Geomagnetic Fluctuations with Periods from 1 s to 60 min. Space Weather, 19 (11): e2021SW002. ISSN 1542-7390

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

Item Type:
Journal Article
Journal or Publication Title:
Space Weather
Additional Information:
This is the peer reviewed version of the following article: N. C. Rogers, J. A. Wild, E. F. Eastoe, J. Hübert (2021), Climatological Statistics of Extreme Geomagnetic Fluctuations With Periods From 1 s to 60 min. Space Weather. doi: 10.1029/2021SW002824 which has been published in final form at This article may be used for non-commercial purposes in accordance With Wiley Terms and Conditions for self-archiving.
Uncontrolled Keywords:
?? geomagnetic fluctuationsgeomagnetically induced currents (gic)extreme value theoryspace weatherspace and planetary sciencegeophysicsatmospheric science ??
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Deposited On:
08 Nov 2021 12:30
Last Modified:
19 Jun 2024 00:41