Reversals and excursions of the geodynamo

Abstract

Using palaeomagnetic records, the time-dependence and morphology of the Earth's magnetic field can be studied over geological timescales. In the temporal domain the magnetic field displays a great deal of irregular behaviour, most spectacularly in the form of occasional reversals and excursions. However, in the spatial domain the field displays some persistent asymmetry, not only during stable nontransitional periods but, quite remarkably, during polarity transitions themselves. These observations may indicate that the Earth's liquid iron outer core is coupled to both the solid inner core and the overlying mantle. An understanding of these effects is a prerequisite to solving the magnetohydrodynamic equations describing the geodynamo.