Understanding Hemispheric Asymmetries of the Auroral Electrojets

Abstract:

We present results from a comprehensive statistical analysis of ground magnetic field data to reveal the characteristics of the conjugacy or non-conjugacy of the ionospheric electrojet system. Our current understanding of the auroral electrojet system as well as modelling efforts and calculations of key parameters are almost solely based on northern hemisphere observations. The inherent assumption is that there are 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 477 events (magnetic bays) for which the ground perturbations measured at the northern and the southern stations are highly uncorrelated. The events have durations of 30-400 minutes and typical magnitudes of 250 nT. We have determined the dependence on solar induced conductance, tilt angle, location (magnetic local time and magnetic latitude) and IMF conditions. To determine cause and effect we have tested four published hypothesis claiming to explain our observations. We find that while the solar induced conductivity plays a key role it does not tell the entire story. Neither, tilt angle or IMF conditions provide complete explanations and we interpret this as indicative that the electrojet system is not completely externally controlled or reversely that internal magnetospheric processes play a key role.