Publication 81
A simple method for deriving the uniform field MT responses in auroral zones
Jones, A.G. and J. Spratt
Abstract
Source field effects in magnetotelluric data acquired at high geomagnetic latitudes can result in
erroneous interpretations of Earth conductivity structure deep within the mantle. This paper
describes a simple technique most appropriate for a region that is dominantly one-dimensional (1-D)
and uses the vertical magnetic field variations for identifying intervals of likely low contamination
by non-uniform sources. Times are chosen when the variations stay within prescribed limits defined
on the basis of a histogram of the variations for the whole recording interval. An example is given
showing application of the method for data from a site under the auroral oval at a time when solar
activity was at its lowest for the last solar cycle. A model derived from the responses obtained by
processing all available data implies a decrease in resistivity at about 350 km to about 100 ohm.m.
In contrast, the model obtained from low activity interval responses shows a less rapid decrease in
resistivity, without a change at around the 410 km phase boundary. The responses obtained from all data
can be explained by the influence of a source with an average wavelength of 3,000 km.
Source
Earth, Planets & Space, 54, 443-450, 2002.
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Alan G Jones / 10 June 2004 /
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