C.C. Finlay and A. Jackson
Department of Earth Sciences, University of Leeds, UK.
The model gufm1 embodies our most detailed knowledge of how the geomagnetic field has varied in both space and time at the core-mantle boundary. The information it contains has, however, not yet been fully exploited. In particular, little attention has been paid to the non-steady field behaviour evident in the Atlantic hemisphere, and the origin and dynamics of prominent flux features in this region are poorly understood. Here we investigate their behaviour since 1590 and attempt to determine dominant wavelengths, frequencies and phase velocities of the motions. In order to characterise the propagation of flux features we implement techniques successfully employed in both meteorology and oceanography for the study of planetary waves. We consider the space-time variation of the radial magnetic field at the core-mantle boundary by taking a series of slices from a longitude, latitude, time cuboid of data. Of particular interest are longitude verses time (or Hovmuller) diagrams which illustrate the zonal motion of non-axisymmetric features. We will present the results of a two dimensional wavenumber/frequency Fourier analysis which highlights the different spectral components in our space-time diagrams. Peaks in these spectra correspond to the dominant components in the propagating signal and can be used to compute phase velocities. These results will provide a guide to geophysically realistic properties of drifting flux features which are likely be present in Earth-like 3D geodynamo simulations.