Robust processing of magnetotelluric data from the auroral zone
Garcia, X., A.D. Chave and A.G. Jones
Magnetotelluric (MT) data acquired during September-October, 1994, in
northern Canada, were strongly influenced by
non-uniform source field contributions from the
auroral electrojet, and especially by intense auroral episodes.
The largest effect on the estimate of the magnetotelluric impedance tensor
elements was during intervals of highest magnetic activity, which primarily
correlated with high auroral activity and was observed during local nighttime.
In comparison, during the day the effect on the normal magnetotelluric
impedance tensor response was usually, but not always, small.
A robust controlled-leverage processing algorithm was applied to
these data in an attempt to extract the stable uniform field estimates
of the impedance.
The differences between nonrobust and robust processing of the entire data
set is compared to that obtained after dividing the time series into
daytime and nighttime segments.
The nonrobust estimate using
all data is controlled by the nocturnal data, which are, in turn,
dominated by non-uniform source effects.
processing of only the daytime data fails to recover a useful
There is little difference between the robust response for the
entire and daytime data provided that the fraction of auroral activity is not
large, i.e., in excess of half of the available data series.
In addition, examination of the time-dependence of the
response functions shows that the strongest bias is observed
during the initial quarter of an auroral event.
J. Geomagn. Geoelectr., 49, 1451-1468, 1997.
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Alan G Jones / 10 June 2004 /