[inquest]

But at least with the core-convection hypothesis there's at least a somewhat plausible explanation, namely that the gyres change direction -or- perhaps that the strength of one gyre overcomes the strength of the other rotating in the opposite direction, and thus its field becomes the dominant field.

[RightWhale]

It seems like, and this is a gut feeling, core convection would be too slow and too stable to change quickly enough to correspond with fluctuations and known reversals in the magfield. Something more mobile would be needed. Something that can change quickly and often.