A new technique for determining Substorm Onsets and Phases from Indices of the Electrojet (SOPHIE)

Forsyth, C., Rae, Jonathan, Coxon, John, Freeman, M. P., Jackman, C. M., Gjerloev, J. and Fazakerley, A. N. (2015) A new technique for determining Substorm Onsets and Phases from Indices of the Electrojet (SOPHIE). Journal of Geophysical Research: Space Physics, 120 (12). pp. 10592-10606. ISSN 2169-9380

JGR Space Physics - 2015 - Forsyth - A new technique for determining Substorm Onsets and Phases from Indices of the.pdf - Published Version
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Official URL: https://doi.org/10.1002/2015JA021343


We present a new quantitative technique that determines the times and durations of substorm expansion and recovery phases and possible growth phases based on percentiles of the rate of change of auroral electrojet indices. By being able to prescribe different percentile values, we can determine the onset and duration of substorm phases for smaller or larger variations of the auroral index or indeed any auroral zone ground-based magnetometer data. We apply this technique to the SuperMAG AL (SML) index and compare our expansion phase onset times with previous lists of substorm onsets. We find that more than 50% of events in previous lists occur within 20min of our identified onsets. We also present a comparison of superposed epoch analyses of SML based on our onsets identified by our technique and existing onset lists and find that the general characteristics of the substorm bay are comparable. By prescribing user-defined thresholds, this automated, quantitative technique represents an improvement over any visual identification of substorm onsets or indeed any fixed threshold method.

Item Type: Article
Additional Information: Funding information: C.F. and I.J.R. are funded in part by Natural Environment Research Council (NERC) grants NE/L007495/1 and NE/M00886X/1 and IJR by Science and Technology Facilities Council (STFC) grant ST/L000563/1. C.M.J. and J.C.C. are funded by NERC grant NE/L007177/1. C. M.J. is also supported by an STFC Ernest Rutherford Fellowship. M.P.F.''s contribution is funded by NERC grant NE/L006456/1. A.N.F. is funded by STFC grants ST/K000977/1 and ST/L005638/1.
Uncontrolled Keywords: auroral indices, onset, phases, substorm
Subjects: F600 Geology
F800 Physical and Terrestrial Geographical and Environmental Sciences
Department: Faculties > Engineering and Environment > Mathematics, Physics and Electrical Engineering
Depositing User: Rachel Branson
Date Deposited: 15 Feb 2022 16:26
Last Modified: 15 Feb 2022 16:30
URI: http://nrl.northumbria.ac.uk/id/eprint/48477

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