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Temporal and spatial dynamics of the regions 1 and 2 Birkeland currents during substorms

Temporal and spatial dynamics of the regions 1 and 2 Birkeland currents during substorms
Temporal and spatial dynamics of the regions 1 and 2 Birkeland currents during substorms

We use current density data from the Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE) to identify the location of maximum region 1 current at all magnetic local times (MLTs). We term this location the R1 oval. Comparing the R1 oval location with particle precipitation boundaries identified in DMSP data, we find that the R1 oval is located on average within 1° of particle signatures associated with the open/closed field line boundary (OCB) across dayside and nightside MLTs. We hence conclude that the R1 oval can be used as a proxy for the location of the OCB. Studying the amount of magnetic flux enclosed by the R1 oval during the substorm cycle, we find that the R1 oval flux is well organized by it: during the growth phase the R1 oval location moves equatorward as the amount of magnetic flux increases whereas after substorm expansion phase onset significant flux closure occurs as the R1 current location retreats to higher latitudes. For about 15 min after expansion phase onset, the amount of open magnetic flux continues to increase indicating that dayside reconnection dominates over nightside reconnection. In the current density data, we find evidence of the substorm current wedge and also show that the dayside R1 currents are stronger than their nightside counterpart during the substorm growth phase, whereas after expansion phase onset, the nightside R1 currents dominate. Our observations of the current distribution and OCB movement during the substorm cycle are in excellent agreement with the expanding/contracting polar cap paradigm. Key Points Region 1 current location is proxy for open/closed field line boundary Average dynamics of the substorm current wedge are shown using AMPERE Dayside FACs are stronger during growth phase, nightside currents after onset

birkeland currents, expanding/contracting polar cap paradigm, region 1/region 2 current, substorm current wedge
2169-9380
3007-3016
Clausen, L. B.N.
7ab01029-f55b-431b-911e-8e0f599ef534
H. Baker, J. B.
26607d0d-8c83-4d9b-90df-031abe9430b4
Ruohoniemi, J. M.
a6f2f18f-d6d5-4fa6-93a9-4114c212326d
Milan, S. E.
b6dd5367-b0c4-4f30-953a-f2d13078d656
Coxon, J. C.
566baea5-6a30-4855-bde3-a09c115efde4
Wing, S.
ef9fcef3-6d9a-407d-bd54-09b27f1382ba
Ohtani, S.
67df7fff-0ba4-4dd0-ac9c-af1215c03592
Anderson, B. J.
c30e4de5-7757-4c54-a05d-43369e879c0c
Clausen, L. B.N.
7ab01029-f55b-431b-911e-8e0f599ef534
H. Baker, J. B.
26607d0d-8c83-4d9b-90df-031abe9430b4
Ruohoniemi, J. M.
a6f2f18f-d6d5-4fa6-93a9-4114c212326d
Milan, S. E.
b6dd5367-b0c4-4f30-953a-f2d13078d656
Coxon, J. C.
566baea5-6a30-4855-bde3-a09c115efde4
Wing, S.
ef9fcef3-6d9a-407d-bd54-09b27f1382ba
Ohtani, S.
67df7fff-0ba4-4dd0-ac9c-af1215c03592
Anderson, B. J.
c30e4de5-7757-4c54-a05d-43369e879c0c

Clausen, L. B.N., H. Baker, J. B., Ruohoniemi, J. M., Milan, S. E., Coxon, J. C., Wing, S., Ohtani, S. and Anderson, B. J. (2013) Temporal and spatial dynamics of the regions 1 and 2 Birkeland currents during substorms. Journal of Geophysical Research: Space Physics, 118 (6), 3007-3016. (doi:10.1002/jgra.50288).

Record type: Article

Abstract

We use current density data from the Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE) to identify the location of maximum region 1 current at all magnetic local times (MLTs). We term this location the R1 oval. Comparing the R1 oval location with particle precipitation boundaries identified in DMSP data, we find that the R1 oval is located on average within 1° of particle signatures associated with the open/closed field line boundary (OCB) across dayside and nightside MLTs. We hence conclude that the R1 oval can be used as a proxy for the location of the OCB. Studying the amount of magnetic flux enclosed by the R1 oval during the substorm cycle, we find that the R1 oval flux is well organized by it: during the growth phase the R1 oval location moves equatorward as the amount of magnetic flux increases whereas after substorm expansion phase onset significant flux closure occurs as the R1 current location retreats to higher latitudes. For about 15 min after expansion phase onset, the amount of open magnetic flux continues to increase indicating that dayside reconnection dominates over nightside reconnection. In the current density data, we find evidence of the substorm current wedge and also show that the dayside R1 currents are stronger than their nightside counterpart during the substorm growth phase, whereas after expansion phase onset, the nightside R1 currents dominate. Our observations of the current distribution and OCB movement during the substorm cycle are in excellent agreement with the expanding/contracting polar cap paradigm. Key Points Region 1 current location is proxy for open/closed field line boundary Average dynamics of the substorm current wedge are shown using AMPERE Dayside FACs are stronger during growth phase, nightside currents after onset

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More information

Accepted/In Press date: 17 April 2013
e-pub ahead of print date: 20 April 2013
Published date: June 2013
Keywords: birkeland currents, expanding/contracting polar cap paradigm, region 1/region 2 current, substorm current wedge

Identifiers

Local EPrints ID: 430689
URI: http://eprints.soton.ac.uk/id/eprint/430689
ISSN: 2169-9380
PURE UUID: e03f2aeb-9099-40f7-af67-379d74df898a
ORCID for J. C. Coxon: ORCID iD orcid.org/0000-0002-0166-6854

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Date deposited: 08 May 2019 16:30
Last modified: 18 Feb 2021 17:24

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Contributors

Author: L. B.N. Clausen
Author: J. B. H. Baker
Author: J. M. Ruohoniemi
Author: S. E. Milan
Author: J. C. Coxon ORCID iD
Author: S. Wing
Author: S. Ohtani
Author: B. J. Anderson

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