The geomagnetic field is generated deep inside the Earth. Within the molten, electrically
conducting iron core of the Earth, i.e. at a depth of approximately 3000 to 5000 kilometers, a
magnetohydrodynamic dynamo maintains the field. The investigation of such a dynamo process
is one of the great challenges for present geophysics. Of particular interest
are episodic field
reversals of the dominant dipole component observed on geological time scales. The main
challenge in numerical simulations of the geodynamo is how to reach an Earth-like parameter
regime where viscous dissipation is small compared to the Coriolis and magnetic Lorentz forces.
In our working group, we have developed a parallel finite volume method for the numerical
solution of spherical dynamo problems. A small temperature difference
between mantle and core
drives a vigorous chaotic flow in the molten core of the Earth. An
initially small magnetic field is
amplified by induction currents until a statistical equilibrium is
reached. The figure displays an
isosurface of the absolute value of the magnetic field strength vector
within the core. In each
hemisphere, the magnetic field at the core mantle boundary is
concentrated in four flux bundles
corresponding to flow cyclones aligned parallel to the axis of
rotation. A field continuation of the
geomagnetic field to the core mantle boundary reveals a similar configuration. In additional
simulations, we explore the transition to small-scale flows by reducing viscous dissipation.
(Helmut Harder, Stephan Stellmach, Ulrich Hansen, Institute of Geophysics,
University of Münster)
Sabine Höfler-Thierfeldt