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  • 2021SW002824 accepted MS

    Rights statement: 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 https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2021SW002824 This article may be used for non-commercial purposes in accordance With Wiley Terms and Conditions for self-archiving.

    Accepted author manuscript, 5.45 MB, PDF document

    Available under license: CC BY: Creative Commons Attribution 4.0 International License

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

Research output: Contribution to journalJournal articlepeer-review

Published
Article numbere2021SW002824
<mark>Journal publication date</mark>30/11/2021
<mark>Journal</mark>Space Weather
Issue number11
Volume19
Publication StatusPublished
Early online date28/10/21
<mark>Original language</mark>English

Abstract

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.

Bibliographic note

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 https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2021SW002824 This article may be used for non-commercial purposes in accordance With Wiley Terms and Conditions for self-archiving.