simulations for eight cases of different imposed patterns
of heat flux through the core-mantle boundary. The total
heat escaping the core is the same for each case. Solid
red (dashed blue) contours denote greater (lesser) heat
flux than the mean. Time is in terms of magnetic diffusion
time for the core (20,000 yr). Zoom
field behavior is observed for the various heat flux cases.
Some cases reversed frequently (A, C) and one didnŐt reverse
at all (E). Case F almost died: the field intensity (dipole
moment) dropped close to zero and stayed there. In the others
the average intensity ranged from 10 to 75 percent of today's
geomagnetic field strength. Case H has heat flux scaled
to seismic velocity in the lower mantle revealed by deep-Earth
tomography, more heat flowing into higher-velocity mantle
where temperature is thought to be lower.