University of Leicester
Browse

Occurrence and Causes of Large dB/dt Events and AL Bays in the Pre-Midnight and Dawn Sectors

Download (6.43 MB)
journal contribution
posted on 2024-10-14, 12:09 authored by Stephen MilanStephen Milan, GE Bower, AL Fleetham, SM Imber, A Schillings, H Opgenoorth, J Gjerloev, LJ Paxton, SK Vines, B Hubert, MR Hairston

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 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 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.

Funding

A Consolidated Grant Proposal for Solar and Planetary Science at the University of Leicester, 2022 - 2025

Science and Technology Facilities Council

Find out more...

Investigating the Drivers of Geomagnetically Induced Currents

Natural Environment Research Council

Find out more...

History

Author affiliation

College of Science & Engineering Physics & Astronomy

Version

  • VoR (Version of Record)

Published in

Journal of Geophysical Research: Space Physics

Volume

129

Issue

10

Publisher

American Geophysical Union (AGU)

issn

2169-9380

eissn

2169-9402

Copyright date

2024

Available date

2024-10-14

Language

en

Deposited by

Professor Stephen Milan

Deposit date

2024-10-10

Usage metrics

    University of Leicester Publications

    Licence

    Exports

    RefWorks
    BibTeX
    Ref. manager
    Endnote
    DataCite
    NLM
    DC