Conjugacy and non-conjugacy of the auroral electrojet system

We present results from a comprehensive statistical analysis of ground magnetic field data aimed at investigating the question: To what extent does the large-scale current system in the northern hemisphere differ from the southern hemisphere and what is the cause of differences? Our current understanding of the auroral electrojet system as well as modeling efforts and calculations of key parameters are largely based on northern hemisphere observations. The inherent assumption is that there is no significant differences between measurements made at magnetically conjugate points in the two hemispheres. In this paper we show that this assumption is often violated. We have identified 921 isolated, intense, and long duration events. About half displaying significant differences between the two hemispheres while the other half are events for which the two hemispheres are in agreement. This dataset allows us to test three possible causes: 1) Solar induced conductivity; 2) IMF conditions (clock angle and IMF By); 3) dipole tilt angle. Neither of these provides a complete explanation. In this presentation we show typical events and test each of the three possible causes.