Dynamic effects of restoring footpoint symmetry on closed magnetic field lines

Reistad, J. P. and Østgaard, N. and Tenfjord, P. and Laundal, K. M. and Snekvik, K. and Haaland, S. and Milan, S. E. and Oksavik, K. and Frey, H. U. and Grocott, A. (2016) Dynamic effects of restoring footpoint symmetry on closed magnetic field lines. Journal of Geophysical Research: Space Physics, 121 (5). pp. 3963-3977. ISSN 2169-9380

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Abstract

Here we present an event where simultaneous global imaging of the aurora from both hemispheres reveals a large longitudinal shift of the nightside aurora of about 3 h, being the largest relative shift reported on from conjugate auroral imaging. This is interpreted as evidence of closed field lines having very asymmetric footpoints associated with the persistent positive y component of the interplanetary magnetic field before and during the event. At the same time, the Super Dual Auroral Radar Network observes the ionospheric nightside convection throat region in both hemispheres. The radar data indicate faster convection toward the dayside in the dusk cell in the Southern Hemisphere compared to its conjugate region. We interpret this as a signature of a process acting to restore symmetry of the displaced closed magnetic field lines resulting in flux tubes moving faster along the banana cell than the conjugate orange cell. The event is analyzed with emphasis on Birkeland currents (BC) associated with this restoring process, as recently described by Tenfjord et al. (2015). Using data from the Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE) during the same conditions as the presented event, the large-scale BC pattern associated with the event is presented. It shows the expected influence of the process of restoring symmetry on BCs. We therefore suggest that these observations should be recognized as being a result of the dynamic effects of restoring footpoint symmetry on closed field lines in the nightside.

Item Type: Journal Article
Journal or Publication Title: Journal of Geophysical Research: Space Physics
Departments: Faculty of Science and Technology > Physics
ID Code: 80242
Deposited By: ep_importer_pure
Deposited On: 29 Jun 2016 08:12
Refereed?: Yes
Published?: Published
Last Modified: 15 Oct 2019 03:45
URI: https://eprints.lancs.ac.uk/id/eprint/80242

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