Publication 113
Source field effects in the auroral zone: Evidence from the Slave craton (NW Canada)
P. Lezeata, A.D. Chave, A.G. Jones, and R.L. Evans
Abstract
We present an investigation of source field effects on the magnetic fields from multiple long period
magnetotelluric (MT) data collected on the floors of lakes throughout the Slave craton (NW Canada) from
1998 to 2000. Monthly and daily power spectra of the magnetic fields suggest a dynamic and seasonally
varying source, with atypical geomagnetic activity in year 2000. Bounded influence MT and GDS responses
were obtained for periods ranging between 80 and 25,000 s over selected monthly time segments.
The responses at periods over 4000 s vary, suggesting source field effects. A frequency domain principal
component (PC) method was applied to the array to investigate the spatial form of the source field
variations. The PC analysis was tested with synthetic data from a regional 3D model with a uniform external
source to study the sensitivity of the eigenvectors to conductivity structure, demonstrating a negligible
influence with increasing penetration depth. We conclude that magnetic fields at periods near one half day
are subject to a 1D polarized source of relatively homogeneous morphology over the survey area during any
month recorded, except for the summer month of July 2000 that had particularly high geomagnetic activity.
In general, the source space approaches two polarizations at periods below one half day, with the dominant
NS component seen quasi-homogeneous over the survey area at periods over 1000 s.
Source
Physics of the Earth and Planetary Interiors, volume, in press, 2007.
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Alan G Jones / 22 July 2007 /
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