INFLUENCE OF THE EARTHS INNER-CORE ON GEOMAGNETIC FLUCTUATIONS AND REVERSALS

IN view of its relatively small size (one-third the radius of the oute r core), many geodynamo models neglect the inner core entirely1, or ot herwise treat it as a non-conducting insulator2,3. In a previous stead y-state model4, we considered some effects of a finitely conducting in ner core, in particular the resulting electromagnetic coupling between inner and outer core. Here we include a prescribed buoyancy force, wh ich is geophysically more realistic, and also yields time-dependent ra ther than time-independent solutions. The field in the finitely conduc ting inner core does not then adjust instantaneously to the field in t he outer core, but has a diffusive timescale of its own of a few thous and years. Rather large, rapid fluctuations in the outer core are then effectively averaged out by the inner core, producing a relatively st able external dipole field. We speculate that a geomagnetic reversal c ould only occur as a result of a particularly large fluctuation, large enough and lasting long enough to reverse the field throughout the in ner core as well.