The 1999 Nature paper presented scenarios in which eight different patterns of heat flux from the core to the mantle were imposed over the core-mantle boundary. The mantle material, although cooler overall, may vary in temperature along the core-mantle boundary. Where the material is coolest, heat is transferred from core to mantle fastest. The simulations kept the total flux across the core-mantle boundary constant but varied the temperature differential between core and mantle in various ways. The outer core surrounds a solid inner core, and the convection in the outer core is thought to be driven by both thermal and compositional buoyancy sources at the inner core boundary, produced as the Earth slowly cools and iron in the fluid alloy solidifies onto the inner core.
Field lines are blue where the field is directed inward and orange where directed outward.
All the cases but one exhibited geomagnetic field reversals. The most Earth-like case as far as reversals go was one in which the heat flux was uniform. We also tried a more geophysically realistic case, in which the heat flux traced the Pacific 'ring of fire,' which showed reversals, but not at the frequency the earth has experienced. The actual effects of the flux across the core-mantle boundary may be a combination of thermodynamic and compositional effects, and only further simulations of this kind will help us distinguish them. For that, Glatzmaier said, the extraordinary computational power now coming on line will certainly be required.