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Interhemispherical Asymmetries in Radial Currents Observed at Low Altitudes by AMPERE During a Geomagnetic Storm

Presented on: December 14, 2020

Presented at: AGU Fall Meeting 2020

Presented by: Robert Strangeway, James Weygand, Andrei Runov, Joachim Raeder, Brian Anderson, Ramon Lopez, Daniel Welling


The structure of Region-1 and Region-2 currents during magnetic storms and substorms can depend on both the drivers for the currents and the underlying properties of the ionosphere-thermosphere. Here we explore a storm-time interval on April 23rd 2012, where the northern polar ionosphere is largely sunlit and the southern polar ionosphere is dark. We use data from AMPERE to compare the radial currents into and out of the northern and southern ionosphere. We find that initially, when the IMF is dominated by positive By, the northern sunlit ionosphere exhibits the currents associated with the DPY current system, but the southern (near terminator) ionosphere shows only weak currents. As the IMF turns southward and the storm progresses the polar cap expands and both ionospheres show the currents expected for standard two-cell convection. In the nightside, however, the dark (southern) ionosphere shows a clear Harang discontinuity, where dusk-side Region-1 currents connect through midnight to dawn-side Region-2 currents. The currents in the northern ionosphere are much weaker near midnight. As the storm progresses the northern hemisphere the near-midnight currents intensify, but show structure that is quite different to the southern ionosphere. In summary the AMPERE data show differences in the radial currents that seem to depend on the underlying ionospheric conductivity. This includes both the currents near the cusp that are most likely directly driven by the solar-wind imposed convection, and the nightside currents that could be a response to fast flows and plasma pressure gradients. Why the current structures appear different can best be addressed through global simulations that allow for north-south asymmetries in the ionosphere.

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