Hi,
You need to look at the direction of movement of the plates.

I am taking a wild guess here, but I suspect that the plasmoids carry both solar polarizations, and usually one is more prominient in the ratio than the other, or the plasma has both negative and positive charge components. Depending on the ratios current either flows one way or the other.
Depending on the direction of current flow it affects the direction of electromotive force. Total guess.

Another guess is that the electromotive force of the plasmoids discharge is interacting with a planetary magnetic field.
If you overlay the planetary magnetic field strength with gravity anomaly mapping you can see that the earth mimics the magnetogram of the sun in regards to magnetic anmalies.


The pinch point over the Indian Ocean is very important z-pinch of plasma.
I am sure there is a better answer.
Tom