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Occurrence and causes of large dB/dt events in the pre-midnight and dawn sectors
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  • Stephen E. Milan,
  • Gemma E. Bower,
  • Amy L Fleetham,
  • Suzanne Mary Imber,
  • Audrey Schillings,
  • Hermann Opgenoorth,
  • Jesper W. Gjerloev,
  • Sarah Kimberly Vines,
  • Larry J. Paxton,
  • Benoit Hubert,
  • Marc R. Hairston
Stephen E. Milan
University of Leicester

Corresponding Author:[email protected]

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Gemma E. Bower
University of Leicester
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Amy L Fleetham
University of Leicester
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Suzanne Mary Imber
University of Leicester
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Audrey Schillings
University of Umeå
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Hermann Opgenoorth
Department of Physics, Umeå University
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Jesper W. Gjerloev
APL-JHU
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Sarah Kimberly Vines
Southwest Research Institute
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Larry J. Paxton
Johns Hopkins University
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Benoit Hubert
University of Liege
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Marc R. Hairston
University of Texas at Dallas
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Abstract

We investigate the causes of large $dB/dt$ events observed by SuperMAG, by comparing with the time-series of different types of geomagnetic activity, or “convection state”, 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 $dB/dt$ 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 favours 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.
29 Apr 2024Submitted to ESS Open Archive
29 Apr 2024Published in ESS Open Archive