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How the IMF ByInduces a Local ByComponent During Northward IMF Bzand Characteristic Timescales

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journal contribution
posted on 2018-05-23, 15:18 authored by P. Tenfjord, N. Østgaard, S. Haaland, K. Snekvik, K. M. Laundal, J. P. Reistad, R. Strangeway, S. E. Milan, M. Hesse, A. Ohma
We use the Lyon-Fedder-Mobarry 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 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 min of the arrival of IMF B y at the bow shock, and it completely reconfigures within 47 min.


This study was supported by the Research Council of Norway/CoE under contract 223252/F50. S. E. Milan was supported by STFC grant ST/K001000/1. We acknowledge the use of NASA/GSFCs 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 ( The CCMC is a multiagency partnership between NASA, AFMC, AFOSR, AFRL, AFWA, NOAA, NSF, and ONR. LFM runs are available as Paul_Tenfjord_081117_1 and Paul_Tenfjord_073117_1a, BATS‐R‐US: ilja_honkonen_011918_1, OpenGGCM: ilja_honkonen_011918_3, and GUMICS: ilja_honkonen_011918_4.



Journal of Geophysical Research: Space Physics, 2018

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


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Journal of Geophysical Research: Space Physics


American Astronomical Society, IOP Publishing





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