ELECTRICAL CONDUCTIVITY IN THE EARTH'S MANTLE INFERRED FROM CHAMP SATELLITE MEASUREMENTS - I. DATA PROCESSING AND 1-D INVERSION

Abstract

A novel time-domain approach to the global electromagnetic induction problem is applied to vector magnetometer data observed by the CHAMP satellite. Data recorded during 11 storm events in 2001-2003 are processed track by track, yielding time-series of spherical harmonic coefficients. The data are then interpreted in terms of 1-D layered electrical conductivity models. The inversion is performed by full search of model parametric space which yields sensitivity of misfit with respect to conductivities of layers and positions of interfaces. In the upper 50 km the inversion solidly recovers a conductive layer corresponding to averaged surface conductance. The conductivity of the lower mantle is established at 6 S m-1 assuming the upper-lower mantle interface is fixed at the seismic-based 670 km boundary. However, the satellite data favour the models with a large jump around 1000 km to unrealistic conductivity values exceeding 103 S m-1. The resolution of the method in the resistive upper mantle sandwiched between conductive crust and lower mantle is poor. Nevertheless, an upper bound of 0.01 S m-1 is suggested by the data. A conductivity increase in the transition zone is not observed. © 2006 The Authors Journal compilation © 2006 RAS.