| Autor: |
Milan, S. E.1 (AUTHOR) steve.milan@le.ac.uk, Bower, G. E.1 (AUTHOR), Fleetham, A. L.1 (AUTHOR), Imber, S. M.1 (AUTHOR), Schillings, A.1,2 (AUTHOR), Opgenoorth, H.1,2 (AUTHOR), Gjerloev, J.3 (AUTHOR), Paxton, L. J.3 (AUTHOR), Vines, S. K.4 (AUTHOR), Hubert, B.5 (AUTHOR), Hairston, M. R.6 (AUTHOR) |
| Předmět: |
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| Zdroj: |
Journal of Geophysical Research. Space Physics. Oct2024, Vol. 129 Issue 10, p1-16. 16p. |
| Abstrakt: |
A necessary condition for the generation of Geomagnetically Induced Currents (GICs) that can pose hazards for technological infrastructure is the occurrence of large, rapid changes in the magnetic field at the surface of the Earth. We investigate the causes of such dB/dt $dB/dt$ events or "spikes" observed by SuperMAG at auroral latitudes, by comparing with the time‐series of different types of geomagnetic activity for the duration of 2010. Spikes are found to occur predominantly in the pre‐midnight and dawn sectors. We find that pre‐midnight spikes are associated with substorm onsets. Dawn sector spikes are not directly associated with substorms, but with auroral activity occurring within the westward electrojet region. Azimuthally‐spaced auroral features drift sunwards, producing Ps6 (10–20 min period) magnetic perturbations on the ground. The magnitude of dB/dt $dB/dt$ is determined by the flow speed in the convection return flow region, which in turn is related to the strength of solar wind‐magnetospheric coupling. Pre‐midnight and dawn sector spikes can occur at the same time, as strong coupling favors both substorms and westward electrojet activity; however, the mechanisms that create them seem somewhat independent. The dawn auroral features share some characteristics with omega bands, but can also appear as north‐south aligned auroral streamers. We suggest that these two phenomena share a single underlying cause. The associated fluctuations in the westward electrojet produce quasi‐periodic negative excursions in the AL index, which can be mis‐identified as recurrent substorm intensifications. Plain Language Summary: Sudden changes in electrical currents flowing in the auroral ionosphere produce magnetic perturbations on the ground, large dB/dt $dB/dt$ "spikes," which can lead to damaging Geomagnetically Induced Currents (GICs) in technological infrastructure. It is known that these spikes occur preferentially in the pre‐midnight local time sector and near dawn, though their exact cause is still poorly understood. In this study we show that pre‐midnight spikes are associated with the well‐known auroral substorm phenomenon which produces sudden southward‐directed perturbations in the magnetic field. Dawn spikes are associated with east‐west spaced auroral features which drift eastwards and produce wave‐like fluctuations in the magnetic field in the east‐west direction. The magnitude of dB/dt $dB/dt$ will depend on the speed at which the forms drift. Pre‐midnight and dawn spikes are not directly related, but can occur together when geomagnetic activity is high. Key Points: Pre‐midnight and dawn spikes in dB/dt $dB/dt$ occur independently; pre‐midnight spikes are associated with substorm onsetsDawn spikes are associated with sunward‐propagating, azimuthally‐spaced auroral features embedded in the westward electrojetFluctuations in AL associated with the dawn sector activity is often mis‐identified as recurrent substorm intensifications [ABSTRACT FROM AUTHOR] |
| Databáze: |
GreenFILE |
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