How the IMF By induces a local By component during northward IMF Bz and 
characteristic timescales

Tenfjord, P.; Østgaard, N.; Haaland, Stein; Snekvik, K.; Laundal, K. M.; Reistad, J. P.; Strangeway, R.; Milan, S. E.; Hesse, M.; Ohma, A.

doi:10.1002/2018JA025186

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How the IMF B_y induces a local B_y component during northward IMF B_z and characteristic timescales

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Haaland, Stein
Department Planets and Comets, Max Planck Institute for Solar System Research, Max Planck Society;

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Citation

Tenfjord, P., Østgaard, N., Haaland, S., Snekvik, K., Laundal, K. M., Reistad, J. P., et al. (2018). How the IMF B_y induces a local B_y component during northward IMF B_z and characteristic timescales. Journal of Geophysical Research: Space Physics, 123(5), 3333-3348. doi:10.1002/2018JA025186.

Cite as: https://hdl.handle.net/21.11116/0000-0001-1DC8-E

Abstract

We use the Lyon‐Fedder‐Mobarry (LFM) global magnetohydrodynamics model to study the effects of the interplanetary magnetic field (IMF) B_y component on the coupling between the solar wind and magnetosphere‐ionosphere system when IMF B_z>0.

We describe the evolution of how a magnetospheric B_y component is induced on closed field lines during these conditions. Starting from dayside lobe reconnection, the magnetic tension on newly reconnected field lines redistribute the open flux asymmetrically between the two hemispheres. This results in asymmetric magnetic energy density in the lobes. Shear flows are induced to restore equilibrium, and these flows are what effectively induces a local B_y component. We show the radial dependence of the induced B_y, and compare the results to the induced B_y during southward IMF conditions.

We also show the response and reconfiguration time of the inner magnetosphere to IMF B_y reversals during northward IMF B_z. A superposed epoch analysis of magnetic field measurements from seven Geostationary Operational Environmental Satellite (GOES) spacecraft at different local times both for negative‐to‐positive, and positive‐to‐negative IMF B_y reversals is presented. We find that the induced B_y responds within 16 minutes of the arrival of IMF B_y at the bow‐shock, and it completely reconfigures within 47 minutes.