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Data obtained from the Australia Wide Array of Geomagnetic Stations (AWAGS) have provided a unique opportunity to investigate the spatial variation of long‐period (Pc 5) ULF wave signal characteristics as a result of plasma waves in low latitudes. Pure state filtering techniques were applied in order to detect highly polarized Pc5 events and derive the wave signal parameters, i.e., the wave frequency, amplitude, polarization, and phase. The results indicate that the Pc 5 signal frequency was virtually independent of latitude and longitude, while the amplitude decreased considerably toward lower latitudes. The spatial variation of the signal polarization was found to be small. However, a statistical analysis of the signal polarization revealed a systematic diurnal variation. Counterclockwise sense of rotation (viewed in the direction of the ambient magnetic field) with the major axis of the polarization ellipse in the northeast quadrant was observed in the local morning, while clockwise sense of rotation with the polarization major axis aligned mainly in the north‐south direction was seen in the local afternoon. Interstation phase analysis yielded small phase variations across the entire station array, indicating azimuthal wave numbers of 1

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The Carpentaria Conductivity Anomaly of western Queensland is a major element in the electrical conductivity structure of the Australian continent. Investigation of it is significant both for its own sake, and as a case history in the general understanding of continental conductivity structure. Following its earlier discovery by reconnaissance magnetometers arrays, detailed magnetotelluric observations were carried out in 1997 along a transect crossing the anomaly between Cloncurry and Julia Creek. The magnetotelluric results define a good conductor within the crust beneath the sediments of the Eromanga Basin. The conductor extends over a depth range of tens of kilometres. This structure, evidently shown also by aeromagnetic and gravity data, is interpreted as the eastern boundary of the Mt Isa Block at a plate suture, which was later covered by the sediments of the Eromanga Basin. Seismic tomographic results show a major gradient in seismic-wave speed in the region. It appears the potential-field, electromagnetic and seismic methods have detected different characteristics of the same geologic structure, with complementary results. The electromagnetic results, new to this paper, define horizontal position well, and give evidence of highly conducting material from the crust to a depth of tens of kilometres. The seismic results extend the depth of the boundary into the upper mantle. The case history supports the hypothesis that the major conductivity anomalies of the geomagnetic deep-sounding method mark continental sutures of fundamental significance in recording the creation of continents.

An array of 29 vector magnetometers was operated in N-NE Brazil from November 1990 until March 1991. We present the analysis of 16 selected quiet days, for which a simple model of an equivalent current distribution for the Sq and EEJ, fits the observed maximum amplitude of the daily variation at midday.In equatorial regions the precise latitude profile of the Sq field is masked by the EEJ. This uncertainty is resolved by assuming that the EEJ, obtained after subtracting the Sq from the daily ranges, should present a ratio of 0.3 for the westward to eastward current. With this constraint, a combined non-linear least squares inversion of Sq and EEJ was used to estimate the parameters of Onwumechili's model of the EEJ current distribution. The H and Z components of the EEJ are jointly inverted and good agreement obtained between the calculated and observed data for all 16 days.The EEJ's main parameters averaged for 16 quiet days were: A total positive current intensity equal to 67 ± 20 (10 3 A) for diurnal range M 4 (or 80 ± 20 (10 3 A) for M 3 ) and a half-width of 403 ± 67 km. The EEJ centre was located at 21 ± 16 km south of the dip equator. The Sq was estimated from several permanent observatories and found to be centred at a mean latitude of 5.5 ± 2 degrees south.