Impacts of Solar Wind Driving on Interhemispheric Asymmetries in the Polar Cap

A key component of solar wind-magnetosphere-ionosphere coupling manifests in the high-latitude field-aligned currents and the spatial extent of open magnetic flux in the polar cap. This in turn drives changes in the cross-polar cap potential (CPCP), like saturation under extreme conditions, and dynamics in the ionospheric electric field, like over- or under-shielding at sub-auroral latitudes. While there have been many studies linking solar wind and interplanetary magnetic field (IMF) driving conditions with the change in the polar cap area, interhemispheric differences have been less well explored. To mitigate uncertainties in connecting the driving conditions to high-latitude field-aligned current characteristics, a criteria of extended, quasi-steady IMF intervals are used for a statistical survey of the AMPERE current density distributions from January 2010 through May 2022. Fits to these distributions following Clausen et al. (2012) are applied in both hemispheres, and then used to derive the area enclosed poleward of the R1 currents. We present an overview of the statistical results of the northern and southern hemisphere current densities, the resulting polar cap areas, and an initial assessment of the CPCP for a given conductance profile. In general, AMPERE observations reveal larger polar cap areas occurring slightly more frequently in the southern hemisphere. Examining the dependencies of the polar cap areas on upstream conditions, there is a clear dependence on IMF B_Z seen for both hemispheres, as expected. However, there is a notable interhemispheric asymmetry in the distribution of polar cap areas as a function of IMF clock angle, specifically for clock angles of 90° versus 270°. Along with the contribution to interhemispheric asymmetries arising from the geomagnetic pole location, these results point to the importance of the dayside conductivity gradient in the closure of the high-latitude field-aligned currents under varying upstream driving conditions.