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On Symmetry and Anisotropy of Earth-core Flows

Authors: N. Schaeffer and M. A. Pais

Ref.: Geophys. Res. Lett. 38, L10309, (2011)

Abstract: Quasi-geostrophic (QG) flows are a recently developed and very promis- ing paradigm for modeling decadal secular variation (SV). Here we exam- ine the effects of allowing anisotropy and departures of the flow from quasi- geostrophy. We perform dedicated numerical experiments of the flow dynam- ics and magnetic induction inside the EarthÂ’s liquid core at time scales char- acteristic of secular variation of the geomagnetic field. Obtained results mo- tivate new flow inversion regularization featuring an equatorially anti-symmetric component superimposed to quasi-geostrophic columns, and stronger lati- tudinal than longitudinal flow gradients. Applying these constraints allows to explain the observed SV for the whole period 1840-2010, and most sig- nificantly, provides a clearly improvement in prediction for decadal length- of-day variations for the period 1980-2000. Furthermore, the trace of the inner- core appears clearly without any assumption for the 1997-2010 period cov- ered by satellite geomagnetic data. Our results support QG being the ap- propriate description of the force balance within the core on decadal time scales and large spatial scales.

DOI: doi:10.1029/2011GL046888