The magnetic field viewed at the core surface. This image has been generated from a mathematical computer model derived from satellite observations of the magnetic field taken by the satellite Magsat in 1980. The core radius is only 3485 km, roughly half that of the Earth's radius. Blue contours indicate the strength of the radial magnetic field entering the core surface, and red contours the strength of the radial field exiting the core surface., and white lines are actual field lines. The picture clearly shows the tilt of the magnetic field away from the rotation axis of the earth by about 10 degrees. This is the major ingredient of the field's deviation from axisymmetry; this lack of axisymmetry is an essential part of dynamo theory, the theory describing how the magnetic field is recreated over time, and is what makes the subject so difficult.
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