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Geomagnetic Pulsations Driving Geomagnetically Induced Currents


AuthorHeyns, M.; Lotz, S.; Gaunt, C.;
Keywordsspace weather; geomagnetic pulsations; geomagnetically induced currents
AbstractGeomagnetically induced currents (GICs) are driven by the geoelectric field induced by fluctuations of Earth s magnetic field. Drivers of intense GICs are often associated with large impulsive events such as coronal mass ejections. To a lesser extent fluctuations from regular oscillations of the geomagnetic field, or geomagnetic pulsations, have also been identified as possible drivers of GICs. In this work we show that these low-frequency pulsations are directly observed in measured GIC data from power networks. Due to the low-pass nature of GICs, Pc5 and lower-frequency pulsations drive significant GICs for an extended duration even at midlatitudes. Longer-period Ps6-type disturbances apparently not typical of midlatitudes are seen with GIC amplitudes comparable to the peak GIC at storm sudden commencement. The quasi-ac (alternating current) nature of the sustained pulsation driving affects the power system response and cannot be properly modeled using only direct current (dc) models. A further consideration is that the often used dB/dt GIC proxy is biased to the sampling rate of the geomagnetic field measurements used. The dB/dt metric does not adequately characterize GIC activity at frequencies in the low ultralow-frequency (ULF) range, and a frequency-weighted proxy akin to geoelectric field should be used instead.
Year of Publication2021
JournalSpace Weather
Volume19
Number of Pagese2020SW002557
Section
Date Published
ISBN
URLhttps://onlinelibrary.wiley.com/doi/abs/10.1029/2020SW002557
DOI10.1029/2020SW002557