North-south asymmetries in magnetospheric and ionospheric plasma circulation

Abstract:

Interaction between the solar wind and the dayside terrestrial magnetopause causes a transfer of energy and momentum from the solar wind to the magnetosphere. Consequently, a large scale circulation - the Dungey cycle - is set up in the magnetosphere. Since the magnetosphere is magnetically connected to the ionosphere, a corresponding circulation of plasma is also set up in the high-latitude ionosphere. Influences from external drivers, in particular the orientation of the radial component of the interplanetary magnetic field as well as daily and seasonal variations in the Earth's tilt angle are known to set up temporal north-south asymmetries in the magnetospheric and ionospheric plasma circulation. There are also persistent north-south asymmetries, which cannot easily be explained by the influence of external drivers. In this presentation, we show examples of such asymmetries in ionospheric convection and asymmetries in magnetospheric lobe density, presumably related to hemispheric asymmetries in ion outflow. We infer that these persistent asymmetries are mainly caused by differences in the strength and configuration of the geomagnetic field between the Northern and Southern Hemispheres. Since the ionosphere is magnetically connected to the magnetosphere, this difference will also be reflected in the magnetosphere in the form of different feedback from the two hemispheres.