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Seasonal and diurnal variations in AMPERE observations of the Birkeland currents compared to modeled results

Seasonal and diurnal variations in AMPERE observations of the Birkeland currents compared to modeled results
Seasonal and diurnal variations in AMPERE observations of the Birkeland currents compared to modeled results
We reduce measurements made by the Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE) to give the total Birkeland (field-aligned) current flowing in both hemispheres in monthly and hourly bins. We analyze these totals using 6 years of data (2010–2015) to examine solar zenith angle-driven variations in the total Birkeland current flowing in both hemispheres, simultaneously, for the first time. A diurnal variation is identified in the total Birkeland current flowing, consistent with variations in the solar zenith angle. A seasonal variation is also identified, with more current flowing in the Northern (Southern) Hemisphere during Bartels rotations in northern (southern) summer. For months close to equinox, more current is found to flow in the Northern Hemisphere, contrary to our expectations. We also conduct the first test of the Milan (2013) model for estimating Birkeland current magnitudes, with modifications made to account for solar contributions to ionospheric conductance based on the observed variation of the Birkeland currents with season and time of day. The modified model, using the value of ?D averaged by Bartels rotation (scaled by 1.7), is found to agree with the observed AMPERE currents, with a correlation of 0.87 in the Northern Hemisphere and 0.86 in the Southern Hemisphere. The improvement over the correlation with dayside reconnection rate is demonstrated to be a significant improvement to the model. The correlation of the residuals is found to be consistent with more current flowing in the Northern Hemisphere. This new observation of systematically larger current flowing in the Northern Hemisphere is discussed in the context of previous results which suggest that the Northern Hemisphere may react more strongly to dayside reconnection than the Southern Hemisphere.
2169-9402
1-14
Coxon, J.C.
566baea5-6a30-4855-bde3-a09c115efde4
Milan, S.E.
4495fdee-b600-43e5-99f7-6193a849b7f5
Carter, J.A.
750f3f36-98fc-4729-acfe-60ded2bd23c1
Clausen, L.B.N.
7ab01029-f55b-431b-911e-8e0f599ef534
Anderson, B.J.
51b61cf6-5745-467f-9efa-5e4bef5f88c7
Korth, H.
8afe22af-96c3-4703-90c0-6a88baa30bc6
Coxon, J.C.
566baea5-6a30-4855-bde3-a09c115efde4
Milan, S.E.
4495fdee-b600-43e5-99f7-6193a849b7f5
Carter, J.A.
750f3f36-98fc-4729-acfe-60ded2bd23c1
Clausen, L.B.N.
7ab01029-f55b-431b-911e-8e0f599ef534
Anderson, B.J.
51b61cf6-5745-467f-9efa-5e4bef5f88c7
Korth, H.
8afe22af-96c3-4703-90c0-6a88baa30bc6

Coxon, J.C., Milan, S.E., Carter, J.A., Clausen, L.B.N., Anderson, B.J. and Korth, H. (2016) Seasonal and diurnal variations in AMPERE observations of the Birkeland currents compared to modeled results Journal of Geophysical Research: Space Physics, 121, pp. 1-14. (doi:10.1002/2015JA022050).

Record type: Article

Abstract

We reduce measurements made by the Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE) to give the total Birkeland (field-aligned) current flowing in both hemispheres in monthly and hourly bins. We analyze these totals using 6 years of data (2010–2015) to examine solar zenith angle-driven variations in the total Birkeland current flowing in both hemispheres, simultaneously, for the first time. A diurnal variation is identified in the total Birkeland current flowing, consistent with variations in the solar zenith angle. A seasonal variation is also identified, with more current flowing in the Northern (Southern) Hemisphere during Bartels rotations in northern (southern) summer. For months close to equinox, more current is found to flow in the Northern Hemisphere, contrary to our expectations. We also conduct the first test of the Milan (2013) model for estimating Birkeland current magnitudes, with modifications made to account for solar contributions to ionospheric conductance based on the observed variation of the Birkeland currents with season and time of day. The modified model, using the value of ?D averaged by Bartels rotation (scaled by 1.7), is found to agree with the observed AMPERE currents, with a correlation of 0.87 in the Northern Hemisphere and 0.86 in the Southern Hemisphere. The improvement over the correlation with dayside reconnection rate is demonstrated to be a significant improvement to the model. The correlation of the residuals is found to be consistent with more current flowing in the Northern Hemisphere. This new observation of systematically larger current flowing in the Northern Hemisphere is discussed in the context of previous results which suggest that the Northern Hemisphere may react more strongly to dayside reconnection than the Southern Hemisphere.

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Accepted/In Press date: 17 April 2016
e-pub ahead of print date: 5 May 2016
Organisations: Astronomy Group

Identifiers

Local EPrints ID: 396135
URI: http://eprints.soton.ac.uk/id/eprint/396135
ISSN: 2169-9402
PURE UUID: ab46c5f1-121b-4e41-b206-284d95a38ad5
ORCID for J.C. Coxon: ORCID iD orcid.org/0000-0002-0166-6854

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Date deposited: 02 Jun 2016 13:47
Last modified: 09 Nov 2017 17:31

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Contributors

Author: J.C. Coxon ORCID iD
Author: S.E. Milan
Author: J.A. Carter
Author: L.B.N. Clausen
Author: B.J. Anderson
Author: H. Korth

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