Abstract
Impulsive geomagnetic variations, latitudinally localized to the auroral zone, have been observed from 2015 to 2020. These impulsive events have been observed mostly in the pre-midnight sector as upward vertical perturbations. Diurnal variations in geomagnetically-triggered harmonic distortion events observed in Hydro-Québec’s Système de Mesure de Décalage Angulaire (SMDA) synchrophasor measurement system found to have a peak in the number of events around midnight. This was similar to diurnal rates of negative Bz geomagnetic impulsive events observed at nearby auroral zone magnetometers. Superposed epoch analysis demonstrates the impulses are regularly associated with increases in harmonic distortion observed at a nearby substation transformer. These large impulsive vertical geomagnetic perturbations appear to be local vortical ionospheric disturbances.
Highlights
The nightside auroral zone ionosphere has long been a subject of study (Fukushima, 1994), being a region of dynamic current structures which interconnect with the inner magnetosphere (McPherron et al, 1973)
We present a statistical study including the occurrence of Bz impulsive events and their relation to geomagnetically induced currents (GIC)
We present evidence that there are regularly occurring vertical impulsive events in the geomagnetic field at auroral zone latitudes
Summary
The nightside auroral zone ionosphere has long been a subject of study (Fukushima, 1994), being a region of dynamic current structures which interconnect with the inner magnetosphere (McPherron et al, 1973). The relatively low frequency of GIC variations, compared to the operating frequency of the power transmission network, means GIC can produce a quasi-DC voltage bias of transformers This can saturate the core of the transformer, producing a harmonic distortion of the transformer voltage (Boteler, 2001). Large impulsive magnetic events may act as another source of GIC If these events were to have a prominent vertical component, Faraday’s Law would indicate that the resultant large vertical magnetic flux changes produced from these events should induce large horizontal geoelectric fields. GIC in transformers within a power transmission network has a spectral content with frequencies much lower than the normal 60 Hz operating frequency of the network They can be approximated as quasi-DC currents. This study uses HD as an indicator of GIC-driven stress on the power transmission network
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