HR: 16:45h
AN: GP12B-04    [PDF]
TI: Constraints on the surface conductance map by 3-D EM induction modeling using ground-based and satellite Sq data
AU: * Vel\'{\i}msk\'{y}, J
EM: velimsky@geo.tamu.edu
AF: Department of Geology and Geophysics, Texas A\&M, Mail stop 3115, College Station, TX 77843 United States
AU: Everett, M E
EM: everett@geo.tamu.edu
AF: Department of Geology and Geophysics, Texas A\&M, Mail stop 3115, College Station, TX 77843 United States
AB: The long-term topic of our research is to determine continental-scale 3-D electrical conductivity variations in Earth's lithosphere and mantle using constraints imposed by ground observatory and satellite-borne magnetometer time series. Recently we have created a database consisting of hourly means of geomagnetic field components observed on quiet days in years 2001 and 2002 at roughly 75 ground observatories and {\O}rsted satellite measurements covering the same time intervals. Forward 3-D time-domain EM global induction modeling of the observations is performed using a spherical harmonic-finite element approach in spherical coordinates. A previously published heterogeneous surface conductance map which reflects the contrast between the resistive continents, intermediate shelves and the highly conductive oceans is an important constituent of the model. The forward code is run with an external excitation that consists of the superposition of several Sq spatiotemporal harmonic functions, thereby simulating induction in the Earth in response to ionospheric Sq current vortices. The 3-D forward calculations produce considerable improvement in the fit of both ground-based and satellite time series compared to that of the optimal 1-D conductivity model derived from daily geomagnetic variations observed at ground stations. This highlights the important role of the oceans and continents in shaping the global Sq response and suggests that the spatial distribution of electrical conductivity in the continental interiors may be resolvable by geomagnetic induction methods. A full 3-D inversion of ground and satellite data, the preliminary results of which are discussed here, is necessary to advance our understanding of the global-scale electrical conductance distribution of the continents and shelves.
DE: 1515 Geomagnetic induction
SC: Geomagnetism and Paleomagnetism [GP]
MN: 2003 Fall Meeting