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|Title:||Birkeland current effects on high-latitude ground magnetic field perturbations|
|Authors:||Laundal, K. M.|
Haaland, S. E.
Gjerloev, J. W.
Reistad, J. P.
Milan, Stephen Eric
Anderson, B. J.
|Publisher:||American Geophysical Union (AGU)|
|Citation:||Geophysical Research Letters, 2015, 42 (18), pp. 7248-7254 (7)|
|Abstract:||Magnetic perturbations on ground at high latitudes are directly associated only with the divergence-free component of the height-integrated horizontal ionospheric current, J⊥,df. Here we show how J⊥,df can be expressed as the total horizontal current J⊥ minus its curl-free component, the latter being completely determined by the global Birkeland current pattern. Thus, in regions where J⊥=0, the global Birkeland current distribution alone determines the local magnetic perturbation. We show with observations from ground and space that in the polar cap, the ground magnetic field perturbations tend to align with the Birkeland current contribution in darkness but not in sunlight. We also show that in sunlight, the magnetic perturbations are typically such that the equivalent overhead current is antiparallel to the convection, indicating that the Hall current system dominates. Thus, the ground magnetic field in the polar cap relates to different current systems in sunlight and in darkness.|
|Rights:||Copyright ©2015. The Authors. This is an open access article under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs License ( http://creativecommons.org/licenses/by-nc-nd/4.0/ ), which permits use and distribution in any medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made.|
|Appears in Collections:||Published Articles, Dept. of Physics and Astronomy|
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