Paleomagnetic observations

source: www.psc.edu/science/glatzmaier.html

Right-click on the image to bring up the Los Alamos National Laboratory animation for a possible reversal process. The lines resemble the magnetic flux wrapped around the core and field lines extend into space. The polarity is color-coded

Magnetic field generation

    Many attempts were made to ex-plain the reasons for a geomagnetic field reversal observed so readily in the magnetization of ferric minerals in ancient lava flows. For the first time, scientists have developed a model that can be considered consistent with obser-vations and a wealth of data gathered for now nearly 200 years (http://www.psc.edu, 1997). According to these authors, the model is a 3D mathematical simu-lation of the dynamics of a magnetic field based on what is known about fluid dynamics, magnetism and the center of the Earth (Glatzmaier, 1997). A supercomputer was fed a circulative program of spherical harmonic equations and Chebyshev polynomial expansions. It differed from other simulations in dimension and data. The rotational speed of the core was configured faster than was previously thought possible. After nearly running for a year equivalent to a time of 36 000 years, the artificial field reversed itself (1997).

    When this simulated reversal occured, the scientists knew, their predictions for the core scenario were right. Immediate investigation of seismic data confirmed that the assumption for the core's high rotational speed really does apply to Earth (Glatzmaier, 1997). The program allows further testing of hypothetical screenplays. Continued simulations with a different set of data for heat flux and rotational speed yielded more insight into how the nature of the differential heat distribution affects the time frame for reversals, and how the magnetic field promotes coupling of the fluid to the solid core creating additional heat (Glatzmaier, 1997). In addition, the model showed that the inner core and the outer core's polarity are opposite of one another and that this arrangement prevents continuous reversal attempts by the convection processes of the outer core (http://www.psc.edu, 1997). Field reversals, say the scientists, are therefore time-varyingly extenuated until a certain amount of energy diffusion has occured. This is a beautiful notion as it demonstrates that the mechanism has a certain stability and will continue as long as energy in form of heat is generated and exchanged.

     Several theories were proposed for the origin of the geomagnetic field among them permanent magnetization, thermoelelectric or gyromagnetic effects (Merrill & McElhinney, 1983). Since we know so little about the Earth's interior, many cannot be entirely excluded. Earth's magnetic field is continuously regenerated. The successful simulation of the reversal demonstrated this.

    The Parker geodynamo theory introduced in 1955 requires a pre-existing magnetic field. Merrill and McElhinney write that magnetic flux is created when hydrodynamic motion of conducting fluids through a magnetic field induces currents which then following Lenz's law oppose the very force that created them. The interactions of a highly conductive substance with the magnetic field serves to strengthen it (1983). Therefore, this geodynamo theory is currently the most accepted proposal as it would be consistent with the fact that amplification occurs. But the theory cannot explain the very reasons for the continuation of the processes that occur between the phase boundaries. Solving for the temperature and pressure realms of the core and boundaries remains one important aspect to the study of the geomagnetic field to which the field itself may provide the clues.