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

A new technique for determining Substorm Onsets and Phases from Indices of the Electrojet (SOPHIE)
A new technique for determining Substorm Onsets and Phases from Indices of the Electrojet (SOPHIE)
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 20 min 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.
2169-9380
10,592-10,606
Forsyth, C.
f3d464cf-81c5-4647-b85a-bc3634bdf076
Rae, I.J.
25677763-0501-4b69-859e-fab930260c69
Coxon, J.C.
566baea5-6a30-4855-bde3-a09c115efde4
Freeman, M.P.
dc974e00-a73d-4d41-a2a8-3c5aebd7a5b5
Jackman, C.M.
9bc3456c-b254-48f1-ade0-912c5b8b4529
Gjerloev, J.
3282d3b3-349c-42e4-be05-aab078086beb
Fazakerley, A.N.
9439164e-a929-4946-980a-57100ac43ec6
Forsyth, C.
f3d464cf-81c5-4647-b85a-bc3634bdf076
Rae, I.J.
25677763-0501-4b69-859e-fab930260c69
Coxon, J.C.
566baea5-6a30-4855-bde3-a09c115efde4
Freeman, M.P.
dc974e00-a73d-4d41-a2a8-3c5aebd7a5b5
Jackman, C.M.
9bc3456c-b254-48f1-ade0-912c5b8b4529
Gjerloev, J.
3282d3b3-349c-42e4-be05-aab078086beb
Fazakerley, A.N.
9439164e-a929-4946-980a-57100ac43ec6

Forsyth, C., Rae, I.J., Coxon, J.C., 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), 10,592-10,606. (doi:10.1002/2015JA021343).

Record type: Article

Abstract

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 20 min 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.

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Forsyth_et_al-2015-Journal_of_Geophysical_Research-_Space_Physics - Version of Record
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e-pub ahead of print date: 14 December 2015
Published date: December 2015

Identifiers

Local EPrints ID: 417609
URI: https://eprints.soton.ac.uk/id/eprint/417609
ISSN: 2169-9380
PURE UUID: cea96b8b-97ba-467c-97e9-a9a1c7439a31
ORCID for J.C. Coxon: ORCID iD orcid.org/0000-0002-0166-6854

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Date deposited: 07 Feb 2018 17:30
Last modified: 15 Oct 2019 00:33

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Contributors

Author: C. Forsyth
Author: I.J. Rae
Author: J.C. Coxon ORCID iD
Author: M.P. Freeman
Author: C.M. Jackman
Author: J. Gjerloev
Author: A.N. Fazakerley

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