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How the IMF B-y induces a B-y component in the closed magnetosphere and how it leads to asymmetric currents and convection patterns in the two hemispheres

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journal contribution
posted on 10.01.2017, 12:17 by P. Tenfjord, N. Østgaard, K. Snekvik, K. M. Laundal, J. P. Reistad, S. Haaland, S. E. Milan
We used the Lyon-Fedder-Mobarry global magnetohydrodynamics model to study the effects of the interplanetary magnetic field (IMF) By component on the coupling between the solar wind and magnetosphere-ionosphere system. When the IMF reconnects with the terrestrial magnetic field with IMF By≠0, flux transport is asymmetrically distributed between the two hemispheres. We describe how By is induced in the closed magnetosphere on both the dayside and nightside and present the governing equations. The magnetosphere imposes asymmetric forces on the ionosphere, and the effects on the ionospheric flow are characterized by distorted convection cell patterns, often referred to as “banana” and “orange” cell patterns. The flux asymmetrically added to the lobes results in a nonuniform induced By in the closed magnetosphere. By including the dynamics of the system, we introduce a mechanism that predicts asymmetric Birkeland currents at conjugate foot points. Asymmetric Birkeland currents are created as a consequence of y directed tension contained in the return flow. Associated with these currents, we expect fast localized ionospheric azimuthal flows present in one hemisphere but not necessarily in the other. We also present current density measurements from Active Magnetosphere and Planetary Electrodynamics Response Experiment that are consistent with this picture. We argue that the induced By produces asymmetrical Birkeland currents as a consequence of asymmetric stress balance between the hemispheres. Such an asymmetry will also lead to asymmetrical foot points and asymmetries in the azimuthal flow in the ionosphere. These phenomena should therefore be treated in a unified way.

Funding

We acknowledge the use of NASA/GSFC’s Space Physics Data Facility for OMNI data. Simulation results have been provided by the Community Coordinated Modeling Center at Goddard Space Flight Center through their public Runs on Request system (http://ccmc.gsfc.nasa.gov). The CCMC is a multiagency partnership between NASA, AFMC, AFOSR, AFRL, AFWA, NOAA, NSF, and ONR (Paul-Tenfjord-032514-1). We thank the AMPERE team and the AMPERE Science Center for providing the Iridium-derived data products. This study was supported by the Research Council of Norway/CoE under contract 223252/F50.

History

Citation

Journal of Geophysical Research: Space Physics, 2015, 120 (11), pp. 9368-9384 (17)

Author affiliation

/Organisation/COLLEGE OF SCIENCE AND ENGINEERING/Department of Physics and Astronomy

Version

VoR (Version of Record)

Published in

Journal of Geophysical Research: Space Physics

Publisher

American Geophysical Union (AGU), Wiley

issn

2169-9402

eissn

2169-9402

Acceptance date

16/10/2015

Copyright date

2015

Available date

10/01/2017

Publisher version

http://onlinelibrary.wiley.com/doi/10.1002/2015JA021579/abstract

Language

en