A numerical model of the geodynamo showing the calculated structure
of the magnetic field on the core-mantle boundary.
Red contours indicate magnetic flux directed radially inwards; blue
contours indicate magnetic flux directed outwards. The
dynamo is driven by thermal convection in the electrically conducting
fluid outer core. Note the bundles of intense magnetic
flux at high latitudes (the source of Earth's magnetic dipole), pairs
of reversed flux patches at low latitudes, low flux above the
north pole and the overall westward drift of the field.