Source field contamination of magnetotelluric data from northern
Canada beneath the auroral zone 

James Cassels, Queen's University, Kingston, Canada
Alan G. Jones, Geological Survey of Canada, Ottawa, Canada

As part of the Lithoprobe Slave-Northern Cordillera Lithospheric Evolution
(SNORCLE) transect investigations, magnetotelluric measurements have been
made in northern Canada within the auroral zone. One survey was during the 
summer time, and the second was during the winter time (March-April). In 
addition, one site was operated at the Yellowknife observatory for over a 
year, and good data exist for the eight month period January - August 1997.

Source-field contamination is a known problem that has been seen in the 
Yellowknife long period MT recordings. Inappropriate response estimation
can lead to resulting models with the depth of the lithosphere/asthenosphere
boundary altered by upwards of 50 km. 

The results of investigating these Yellowknife data for source-field 
contamination will be presented.  The goal is to develop an automatic 
objective scheme for detecting such contamination, and reducing their effects 
on the response function evaluation.