Forsyth, C;
Shortt, M;
Coxon, JC;
Rae, IJ;
Freeman, MP;
Kalmoni, NME;
Jackman, CM;
... Burrell, AG; + view all
(2018)
Seasonal and Temporal Variations of Field-Aligned Currents and Ground Magnetic Deflections During Substorms.
Journal of Geophysical Research: Space Physics
, 123
(4)
pp. 2696-2713.
10.1002/2017JA025136.
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Abstract
Field-aligned currents (FACs), also known as Birkeland currents, are the agents by which energy and momentum are transferred to the ionosphere from the magnetosphere and solar wind. This coupling is enhanced at substorm onset through the formation of the substorm current wedge. Using FAC data from the Active Magnetosphere and Planetary Electrodynamics Response Experiment and substorm expansion phase onsets identified using the Substorm Onsets and Phases from Indices of the Electrojet technique, we examine the Northern Hemisphere FACs in all local time sectors with respect to substorm onset and subdivided by season. Our results show that while there is a strong seasonal dependence on the underlying FACs, the increase in FACs following substorm onset only varies by 10% with season, with substorms increasing the hemispheric FACs by 420 kA on average. Over an hour prior to substorm onset, the dayside currents in the postnoon quadrant increase linearly, whereas the nightside currents show a linear increase starting 20-30 min before onset. After onset, the nightside Region 1, Region 2, and nonlocally closed currents and the SuperMAG AL (SML) index follow the Weimer (1994, https://doi.org/10.1029/93JA02721) model with the same time constants in each season. These results contrast earlier contradictory studies that indicate that substorms are either longer in the summer or decay faster in the summer. Our results imply that, on average, substorm FACs do not change with season but that their relative impact on the coupled magnetosphere-ionosphere system does due to the changes in the underlying currents.
| Type: | Article |
|---|---|
| Title: | Seasonal and Temporal Variations of Field-Aligned Currents and Ground Magnetic Deflections During Substorms |
| Open access status: | An open access version is available from UCL Discovery |
| DOI: | 10.1002/2017JA025136 |
| Publisher version: | http://doi.org/10.1002/2017JA025136 |
| Language: | English |
| Additional information: | Copyright © 2018. The Authors. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited. |
| UCL classification: | UCL UCL > Provost and Vice Provost Offices > UCL BEAMS UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Space and Climate Physics |
| URI: | https://discovery.ucl.ac.uk/id/eprint/10048615 |
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