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Different methods to compute flows at the core-mantle boundary from geomagnetic data

Authors: F. Nogueira, O. Oliveira, M. A. Pais, G. Hulot, J.-L. Le Mouël

Ref.: 26th General Assembly of European Geophysical Society (2001)

Abstract: The flow at a particular epoch can be determined by solving the matricial equation Ax=B, where x is the vector of poloidal and toroidal flow coefficients, B is the data vector of spherical harmonic coefficients of the SV and A is the interaction matrix. This inverse problem is ill-posed in the sense that there exist many possible solutions for the flow. Classical techniques rely on regularization conditions which strongly restrict the space of solutions; typically, they require the kinetic energy of the flow or its roughness to be small. As a consequence, the knowledge of the core surface flow will be biased in favor of simple large scale flows. In this tudy we use genetic algorithms and simulated annealing methods to explore the space of possible solutions in search of different patterns of CMB flows. We obtain a number of different solutions, all of them compatible with the observed geomagnetic surface data. Our results show that the nature of the flow depends strongly on the method used. We present a first attempt to understand the geophysical relevance of our solutions, the role of the different components on the multipole expansion and the influence of the truncation.