Journal of Conference Abstracts

Non-harmonic Downward Continuation of the Earth Magnetic Field in the Lower Mantle

Ludwig Ballani (bal@gfz-potsdam.de), Hans Greiner-Mai (grm@gfz-potsdam.de) & Dietrich Stromeyer (stro@gfz-potsdam.de)

GeoForschungsZentrum Potsdam, Telegrafenberg, Potsdam, D-14473, Germany

Earth rotation and geomagnetic field are clearly correlated in the decadal periode range (10y...100y). Outer-core fluid motions via the electromagnetic core-mantle coupling are assumed to be responsible for this. The modelling of the coupling (Lorentz-) torques requires the downward continuation of the temporally variable magnetic field through the mantle to the core-mantle boundary using time series of the surface magnetic field as boundary values.

This inverse boundary-value problem for the diffusion equation is of the "inverse heat conduction problem" type, which is known to be extremely ill-posed. For its solution, an adapted regularizing procedure based on modern theoretical stability estimates and using a boundary-control approach was developed. Using different assumptions, we calculate several core-mantle boundary field components covering a time interval of about one hundred years.