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Asymmetric ionospheric currents

Dependent Source of Asymmetry

Relative Importance – Unknown


Both the field aligned current patterns and the equivalent ionospheric current (combined Hall and Pedersen) patterns within the auroral oval significantly shift with the changing direction of the interplanetary of the magnetic field. The most significant asymmetries occur within the cusp region current system, where the equivalent current patterns can be reversed between the northern and southern hemispheres, and the Harang region current system, which can be offset in local time between the northern and southern hemispheres [Anderson et al., 2008; Strangeway et al., 2000].

The asymmetric ionospheric currents are primarily dependent the By component of the interplanetary of the magnetic field, which changes the reconnection region in the magnetosphere and lobe magnetic field orientation [Tenfjord et al., 2015].

Variations in the interplanetary magnetic field By component changes the location and extend of the auroral electrojets in both the day side sector and night side sector. Furthermore, the location of the throat of the cusp and entry point becomes distinctly different in the northern and southern hemispheres [Anderson et al., 2008; Strangeway et al., 2000].

The top panel shows the equivalent ionosphere currents in the northern hemisphere (left side) and southern hemisphere (right side) for a strong positive By component of the interplanetary magnetic field. The green arrows display the approximate direction of the equivalent currents in the cusp region in both hemispheres. The bottom panels gives the equivalent ionosphere currents in the northern hemisphere and southern hemisphere for a negative By component of the interplanetary magnetic field. For the negative By direction the shear in the equivalent currents is in the opposite direction of that for the positive By component in the cusp region.

Modeling Capability:

In general, global magnetohydrodynamic (MHD) models with a height-integrated ionospheric electrodynamics model can capture the large-scale behavior of Birkeland currents as a function of IMF By.  However, to the extent to which asymmetries in horizontal currents are captured in these models remains largely unexplored.


Largely unexplored


Largely unexplored


Largely unexplored

Largely unexplored


Strangeway, R. J., Ct T. Russell, C. W. Carlson, J. P. McFadden, R. E. Ergun, M. Temerin, D. M. Klumpar, W. K. Peterson, and T. E. Moore. “Cusp field‐aligned currents and ion outflows.” Journal of Geophysical Research: Space Physics 105, no. A9 (2000): 21129-21141.

Tenfjord, P., N. Østgaard, K. Snekvik, K. M. Laundal, J. P. Reistad, S. Haaland, and S. E. Milan (2015), How the IMF By induces a By component in the closed magnetosphere and how it leads to asymmetric currents and convection patterns in the two hemispheres, J. Geophys. Res. Space Physics, 120, 9368–9384, doi:10.1002/2015JA021579.

Anderson, B. J., H. Korth, C. L. Waters, D. L. Green, and P. Stauning. “Statistical Birkeland current distributions from magnetic field observations by the Iridium constellation.” In Annales Geophysicae, vol. 26, no. 3, pp. 671-687. Copernicus GmbH, 2008.

One Reply to “Ionospheric currents”

Alexa Halford

This news article goes into depth about Birkeland currents and the asymmetries seen during the October 8th 2012 geomagnetic storm. https://cusia.uta.edu/news/ampere-and-swmf-observations-of-interhemispheric-asymmetries-in-birkeland-currents-during-the-8-october-2012-magnetic-storm/

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