LONGITUDINALLY CONFINED GEOMAGNETIC REVERSAL PATHS FROM NONDIPOLAR TRANSITION FIELDS

IT has long been thought that conditions at the boundary between the core and mantle influence the Earth's magnetic field, but the supporting evidence is rather indirect1-3. Recent palaeomagnetic results, suggesting that there are persistent preferred longitudinal paths for the virtual geomagnetic pole (VGP) during reversals4, would provide the first direct evidence of the solid mantle's influence on the core, although their statistical significance has been disputed5,6. The results are potentially exciting because the preferred paths lie close to the Pacific rim, where the present geomagnetic secular variation changes character2,7. Here we present a simple model, based on an extension of a previous theory8, that produces reversals with VGP paths confined within relatively narrow longitude bands despite the transition field having a substantially non-dipolar structure. Thus, although longitude bias of the VGP paths is definitive evidence for core-mantle interaction, simple VGP paths are not evidence of near-dipolar transition fields.