Abstract/Summary

Two recent papers by Troshichev, Stepanov and Sormakov (2023) and by Lockwood (2023) have presented different physical mechanisms that cause instantaneous polar cap indices, measured close to the geomagnetic poles in the north and south hemispheres, to differ even though their overall behaviour is very similar. Several effects are described but the two main mechanisms discussed are the effect of the dawn-dusk (Y) component of the Interplanetary Magnetic Field (IMF) and inductive decoupling of electric fields caused by changes in the magnetic field in the magnetospheric lobes. This paper shows that both papers are correct and that both of the two major mechanisms are active and cause differences between the northern and southern indices. The variations in the differences with fraction of the calendar year and Universal Time are described and explained.