Run electricity around an iron core to generate a magnetic field.
pehaps that large ball of iron rotating and moving through the sun's fields creates our magnetic field, and the poles of it.
The earth is rotaing and moving through the sun's field continuously, and the sun's field may change, depending on who knows what, thus the earth's fields are affected.
My story and i;s sticking to it. :-)
Adding to that, the sun is not a perfect static center in it’s self. The Sun’s “Barycenter” moves around aside from the earth having an elliptical orbit. And we tend to forget that the whole solar system has an orbit around the galactic center. Who knows what influences our whole solar system and earth magnet as we orbit through different galactic magnetic field zones emanating from the galactic center.