HR: 0800h
AN: GP11D-0848    [Abstracts]
TI: Scale-Invariance in Geomagnetic Secular Variation
AU: * Jonkers, A R
EM: jonkers@liv.ac.uk
AF: Dept of Earth and Ocean Sciences, University of Liverpool, 4 Brownlow Street, Liverpool, L69 3GP United Kingdom
AB: The historical geomagnetic field model {\it gufm1} (A.D. 1590-1990, spherical-harmonic expansion up to degree 14 inclusive) is based upon the largest-ever compilation of historical geomagnetic data, and captures geomagnetic change on time scales from years to centuries at the top of the outer core. This surface has been subdivided into grid cells for which the model provided (dipole-detrended) time series of first differences for each of the three orthogonal vector components. Analysis of these fluctuations in terms of various probability distribution functions suggests that power laws can adequately represent the observed, absolute, size-ranked changes over time over a range of (size) scales. Moreover, novel techniques from Complexity Theory allow the estimation of the Hurst parameter (per cell per component), which quantifies the intensity of systemic "memory." Subsequent cluster analysis of cells for a range of significant Hurst threshold values has additionally brought to light spatial power laws in cluster surface areas when ranked by size. Finally, spectral analysis of all power law residuals was used to investigate discrete scale-invariance, i.e., the possible existence of preferred physical length scales in the geodynamo process. Positive evidence in the historical model seems to correspond with similar traits found in the geomagnetic reversal record (present to Cretaceous superchron inclusive). The combined profile of spatial and temporal power laws, intense systemic memory, and characteristic length scales appears to suggest that the geodynamo may be operating as an out-of-equilibrium system just below the threshold of chaos (i.e., in a state of self-organised criticality). Reversals and historical secular variation could thereby be considered expressions of the same underlying process.
DE: 1560 Time variations--secular and long term
SC: Geomagnetism and Paleomagnetism [GP]
MN: 2004 AGU Fall Meeting